Add link, images (resource)

This is still some messy code that needs cleaning up, but it adds support for
links and images, of the resource kind (`[a](b)`).
References (`[a][b]`) are parsed and will soon be supported, but need matching.

*   Fix bug to pad percent-encoded bytes when normalizing urls
*   Fix bug with escapes counting as balancing in destination
*   Add `space_or_tab_one_line_ending`, to parse whitespace including up to
    one line ending (but not a blank line)
*   Add `ParserState` to share codes, definitions, etc

7 files changed, 951 insertions, 274 deletions

diff --git a/tests/character_escape.rs b/tests/character_escape.rs
index e4f23d2..3e3e839 100644
--- a/tests/character_escape.rs
+++ b/tests/character_escape.rs
@@ -61,12 +61,11 @@ fn character_escape() {
         "should not escape in flow html"
     );
 
-    // To do: link (reference).
-    // assert_eq!(
-    //     micromark("[foo](/bar\\* \"ti\\*tle\")"),
-    //     "<p><a href=\"/bar*\" title=\"ti*tle\">foo</a></p>",
-    //     "should escape in resource and title"
-    // );
+    assert_eq!(
+        micromark("[foo](/bar\\* \"ti\\*tle\")"),
+        "<p><a href=\"/bar*\" title=\"ti*tle\">foo</a></p>",
+        "should escape in resource and title"
+    );
 
     // To do: link (reference).
     // assert_eq!(
diff --git a/tests/character_reference.rs b/tests/character_reference.rs
index 136ce17..3d2111e 100644
--- a/tests/character_reference.rs
+++ b/tests/character_reference.rs
@@ -55,14 +55,13 @@ fn character_reference() {
         "should not care about character references in html"
     );
 
-    // To do: link (resource).
-    // assert_eq!(
-    //     micromark("[foo](/f&ouml;&ouml; \"f&ouml;&ouml;\")"),
-    //     "<p><a href=\"/f%C3%B6%C3%B6\" title=\"föö\">foo</a></p>",
-    //     "should support character references in resource URLs and titles"
-    // );
+    assert_eq!(
+        micromark("[foo](/f&ouml;&ouml; \"f&ouml;&ouml;\")"),
+        "<p><a href=\"/f%C3%B6%C3%B6\" title=\"föö\">foo</a></p>",
+        "should support character references in resource URLs and titles"
+    );
 
-    // To do: link (resource).
+    // To do: link (reference).
     // assert_eq!(
     //     micromark("[foo]: /f&ouml;&ouml; \"f&ouml;&ouml;\"\n\n[foo]"),
     //     "<p><a href=\"/f%C3%B6%C3%B6\" title=\"föö\">foo</a></p>",
@@ -101,12 +100,11 @@ fn character_reference() {
     //     "should not support character references as construct markers (2)"
     // );
 
-    // To do: link (resource).
-    // assert_eq!(
-    //     micromark("[a](url &quot;tit&quot;)"),
-    //     "<p>[a](url &quot;tit&quot;)</p>",
-    //     "should not support character references as construct markers (3)"
-    // );
+    assert_eq!(
+        micromark("[a](url &quot;tit&quot;)"),
+        "<p>[a](url &quot;tit&quot;)</p>",
+        "should not support character references as construct markers (3)"
+    );
 
     assert_eq!(
         micromark("foo&#10;&#10;bar"),
diff --git a/tests/image.rs b/tests/image.rs
new file mode 100644
index 0000000..a54c8d2
--- /dev/null
+++ b/tests/image.rs
@@ -0,0 +1,229 @@
+extern crate micromark;
+use micromark::micromark;
+
+#[test]
+fn image() {
+    assert_eq!(
+        micromark("[link](/uri \"title\")"),
+        "<p><a href=\"/uri\" title=\"title\">link</a></p>",
+        "should support links"
+    );
+    assert_eq!(
+        micromark("![foo](/url \"title\")"),
+        "<p><img src=\"/url\" alt=\"foo\" title=\"title\" /></p>",
+        "should support image w/ resource"
+    );
+
+    // To do: attention.
+    // assert_eq!(
+    //     micromark("[foo *bar*]: train.jpg \"train & tracks\"\n\n![foo *bar*]"),
+    //     "<p><img src=\"train.jpg\" alt=\"foo bar\" title=\"train &amp; tracks\" /></p>",
+    //     "should support image as shortcut reference"
+    // );
+
+    // To do: tags in images.
+    // assert_eq!(
+    //     micromark("![foo ![bar](/url)](/url2)"),
+    //     "<p><img src=\"/url2\" alt=\"foo bar\" /></p>",
+    //     "should “support” images in images"
+    // );
+
+    // To do: tags in images.
+    // assert_eq!(
+    //     micromark("![foo [bar](/url)](/url2)"),
+    //     "<p><img src=\"/url2\" alt=\"foo bar\" /></p>",
+    //     "should “support” links in images"
+    // );
+
+    // To do: tags in images.
+    // assert_eq!(
+    //     micromark("[foo *bar*]: train.jpg \"train & tracks\"\n\n![foo *bar*][]"),
+    //     "<p><img src=\"train.jpg\" alt=\"foo bar\" title=\"train &amp; tracks\" /></p>",
+    //     "should support “content” in images"
+    // );
+
+    // To do: tags in images, attention, references.
+    // assert_eq!(
+    //     micromark("[FOOBAR]: train.jpg \"train & tracks\"\n\n![foo *bar*][foobar]"),
+    //     "<p><img src=\"train.jpg\" alt=\"foo bar\" title=\"train &amp; tracks\" /></p>",
+    //     "should support “content” in images"
+    // );
+
+    assert_eq!(
+        micromark("![foo](train.jpg)"),
+        "<p><img src=\"train.jpg\" alt=\"foo\" /></p>",
+        "should support images w/o title"
+    );
+
+    assert_eq!(
+        micromark("My ![foo bar](/path/to/train.jpg  \"title\"   )"),
+        "<p>My <img src=\"/path/to/train.jpg\" alt=\"foo bar\" title=\"title\" /></p>",
+        "should support images w/ lots of whitespace"
+    );
+
+    assert_eq!(
+        micromark("![foo](<url>)"),
+        "<p><img src=\"url\" alt=\"foo\" /></p>",
+        "should support images w/ enclosed destinations"
+    );
+
+    assert_eq!(
+        micromark("![](/url)"),
+        "<p><img src=\"/url\" alt=\"\" /></p>",
+        "should support images w/ empty labels"
+    );
+
+    // To do: references.
+    // assert_eq!(
+    //     micromark("[bar]: /url\n\n![foo][bar]"),
+    //     "<p><img src=\"/url\" alt=\"foo\" /></p>",
+    //     "should support full references (1)"
+    // );
+
+    // To do: references.
+    // assert_eq!(
+    //     micromark("[BAR]: /url\n\n![foo][bar]"),
+    //     "<p><img src=\"/url\" alt=\"foo\" /></p>",
+    //     "should support full references (2)"
+    // );
+
+    // To do: references.
+    // assert_eq!(
+    //     micromark("[foo]: /url \"title\"\n\n![foo][]"),
+    //     "<p><img src=\"/url\" alt=\"foo\" title=\"title\" /></p>",
+    //     "should support collapsed references (1)"
+    // );
+
+    // To do: references, attention, tags in images.
+    // assert_eq!(
+    //     micromark("[*foo* bar]: /url \"title\"\n\n![*foo* bar][]"),
+    //     "<p><img src=\"/url\" alt=\"foo bar\" title=\"title\" /></p>",
+    //     "should support collapsed references (2)"
+    // );
+
+    // To do: references.
+    // assert_eq!(
+    //     micromark("[foo]: /url \"title\"\n\n![Foo][]"),
+    //     "<p><img src=\"/url\" alt=\"Foo\" title=\"title\" /></p>",
+    //     "should support case-insensitive labels"
+    // );
+
+    // To do: references.
+    // assert_eq!(
+    //     micromark("[foo]: /url \"title\"\n\n![foo] \n[]"),
+    //     "<p><img src=\"/url\" alt=\"foo\" title=\"title\" />\n[]</p>",
+    //     "should not support whitespace between sets of brackets"
+    // );
+
+    // To do: references.
+    // assert_eq!(
+    //     micromark("[foo]: /url \"title\"\n\n![foo]"),
+    //     "<p><img src=\"/url\" alt=\"foo\" title=\"title\" /></p>",
+    //     "should support shortcut references (1)"
+    // );
+
+    // To do: references, tags in images, attention.
+    // assert_eq!(
+    //     micromark("[*foo* bar]: /url \"title\"\n\n![*foo* bar]"),
+    //     "<p><img src=\"/url\" alt=\"foo bar\" title=\"title\" /></p>",
+    //     "should support shortcut references (2)"
+    // );
+
+    assert_eq!(
+        micromark("[[foo]]: /url \"title\"\n\n![[foo]]"),
+        "<p>[[foo]]: /url &quot;title&quot;</p>\n<p>![[foo]]</p>",
+        "should not support link labels w/ unescaped brackets"
+    );
+
+    // To do: references.
+    // assert_eq!(
+    //     micromark("[foo]: /url \"title\"\n\n![Foo]"),
+    //     "<p><img src=\"/url\" alt=\"Foo\" title=\"title\" /></p>",
+    //     "should support case-insensitive label matching"
+    // );
+
+    // To do: references.
+    // assert_eq!(
+    //     micromark("[foo]: /url \"title\"\n\n!\\[foo]"),
+    //     "<p>![foo]</p>",
+    //     "should “support” an escaped bracket instead of an image"
+    // );
+
+    // To do: references.
+    // assert_eq!(
+    //     micromark("[foo]: /url \"title\"\n\n\\![foo]"),
+    //     "<p>!<a href=\"/url\" title=\"title\">foo</a></p>",
+    //     "should support an escaped bang instead of an image, but still have a link"
+    // );
+
+    // Extra
+    assert_eq!(
+        micromark("![foo]()"),
+        "<p><img src=\"\" alt=\"foo\" /></p>",
+        "should support images w/o destination"
+    );
+
+    assert_eq!(
+        micromark("![foo](<>)"),
+        "<p><img src=\"\" alt=\"foo\" /></p>",
+        "should support images w/ explicit empty destination"
+    );
+
+    assert_eq!(
+        micromark("![](example.png)"),
+        "<p><img src=\"example.png\" alt=\"\" /></p>",
+        "should support images w/o alt"
+    );
+
+    assert_eq!(
+        micromark("![alpha](bravo.png \"\")"),
+        "<p><img src=\"bravo.png\" alt=\"alpha\" /></p>",
+        "should support images w/ empty title (1)"
+    );
+
+    assert_eq!(
+        micromark("![alpha](bravo.png '')"),
+        "<p><img src=\"bravo.png\" alt=\"alpha\" /></p>",
+        "should support images w/ empty title (2)"
+    );
+
+    assert_eq!(
+        micromark("![alpha](bravo.png ())"),
+        "<p><img src=\"bravo.png\" alt=\"alpha\" /></p>",
+        "should support images w/ empty title (3)"
+    );
+
+    assert_eq!(
+    micromark("![&amp;&copy;&](example.com/&amp;&copy;& \"&amp;&copy;&\")"),
+    "<p><img src=\"example.com/&amp;%C2%A9&amp;\" alt=\"&amp;©&amp;\" title=\"&amp;©&amp;\" /></p>",
+    "should support character references in images"
+  );
+
+    // Extra
+    // See: <https://github.com/commonmark/commonmark.js/issues/192>
+    assert_eq!(
+        micromark("![](<> \"\")"),
+        "<p><img src=\"\" alt=\"\" /></p>",
+        "should ignore an empty title"
+    );
+
+    // To do: extensions
+    // assert_eq!(
+    //   micromark("![x]()", {extensions: [{disable: {null: ["labelStartImage"]}}]}),
+    //   "<p>!<a href=\"\">x</a></p>",
+    //   "should support turning off label start (image)"
+    // );
+
+    assert_eq!(
+        micromark("![](javascript:alert(1))"),
+        "<p><img src=\"\" alt=\"\" /></p>",
+        "should ignore non-http protocols by default"
+    );
+
+    // To do: extensions
+    // assert_eq!(
+    //   micromark("![](javascript:alert(1))", {allowDangerousProtocol: true}),
+    //   "<p><img src=\"javascript:alert(1)\" alt=\"\" /></p>",
+    //   "should allow non-http protocols w/ `allowDangerousProtocol`"
+    // );
+}
diff --git a/tests/link_resource.rs b/tests/link_resource.rs
new file mode 100644
index 0000000..b1e1905
--- /dev/null
+++ b/tests/link_resource.rs
@@ -0,0 +1,464 @@
+extern crate micromark;
+use micromark::{micromark, micromark_with_options, Options};
+
+const DANGER: &Options = &Options {
+    allow_dangerous_html: true,
+    allow_dangerous_protocol: true,
+    default_line_ending: None,
+};
+
+#[test]
+fn link_resource() {
+    assert_eq!(
+        micromark("[link](/uri \"title\")"),
+        "<p><a href=\"/uri\" title=\"title\">link</a></p>",
+        "should support links"
+    );
+
+    assert_eq!(
+        micromark("[link](/uri)"),
+        "<p><a href=\"/uri\">link</a></p>",
+        "should support links w/o title"
+    );
+
+    assert_eq!(
+        micromark("[link]()"),
+        "<p><a href=\"\">link</a></p>",
+        "should support links w/o destination"
+    );
+
+    assert_eq!(
+        micromark("[link](<>)"),
+        "<p><a href=\"\">link</a></p>",
+        "should support links w/ empty enclosed destination"
+    );
+
+    assert_eq!(
+        micromark("[link](/my uri)"),
+        "<p>[link](/my uri)</p>",
+        "should not support links w/ spaces in destination"
+    );
+
+    assert_eq!(
+        micromark("[link](</my uri>)"),
+        "<p><a href=\"/my%20uri\">link</a></p>",
+        "should support links w/ spaces in enclosed destination"
+    );
+
+    assert_eq!(
+        micromark("[link](foo\nbar)"),
+        "<p>[link](foo\nbar)</p>",
+        "should not support links w/ line endings in destination"
+    );
+
+    assert_eq!(
+        micromark_with_options("[link](<foo\nbar>)", DANGER),
+        "<p>[link](<foo\nbar>)</p>",
+        "should not support links w/ line endings in enclosed destination"
+    );
+
+    assert_eq!(
+        micromark("[a](<b)c>)"),
+        "<p><a href=\"b)c\">a</a></p>",
+        "should support links w/ closing parens in destination"
+    );
+
+    assert_eq!(
+        micromark("[link](<foo\\>)"),
+        "<p>[link](&lt;foo&gt;)</p>",
+        "should not support links w/ enclosed destinations w/o end"
+    );
+
+    assert_eq!(
+        micromark_with_options("[a](<b)c\n[a](<b)c>\n[a](<b>c)", DANGER),
+        "<p>[a](&lt;b)c\n[a](&lt;b)c&gt;\n[a](<b>c)</p>",
+        "should not support links w/ unmatched enclosed destinations"
+    );
+
+    assert_eq!(
+        micromark("[link](\\(foo\\))"),
+        "<p><a href=\"(foo)\">link</a></p>",
+        "should support links w/ destinations w/ escaped parens"
+    );
+
+    assert_eq!(
+        micromark("[link](foo(and(bar)))"),
+        "<p><a href=\"foo(and(bar))\">link</a></p>",
+        "should support links w/ destinations w/ balanced parens"
+    );
+
+    assert_eq!(
+        micromark("[link](foo\\(and\\(bar\\))"),
+        "<p><a href=\"foo(and(bar)\">link</a></p>",
+        "should support links w/ destinations w/ escaped parens"
+    );
+
+    assert_eq!(
+        micromark("[link](<foo(and(bar)>)"),
+        "<p><a href=\"foo(and(bar)\">link</a></p>",
+        "should support links w/ enclosed destinations w/ parens"
+    );
+
+    assert_eq!(
+        micromark_with_options("[link](foo\\)\\:)", DANGER),
+        "<p><a href=\"foo):\">link</a></p>",
+        "should support links w/ escapes in destinations"
+    );
+
+    assert_eq!(
+        micromark("[link](#fragment)"),
+        "<p><a href=\"#fragment\">link</a></p>",
+        "should support links w/ destinations to fragments"
+    );
+
+    assert_eq!(
+        micromark("[link](http://example.com#fragment)"),
+        "<p><a href=\"http://example.com#fragment\">link</a></p>",
+        "should support links w/ destinations to URLs w/ fragments"
+    );
+
+    assert_eq!(
+        micromark("[link](http://example.com?foo=3#frag)"),
+        "<p><a href=\"http://example.com?foo=3#frag\">link</a></p>",
+        "should support links w/ destinations to URLs w/ search and fragments"
+    );
+
+    assert_eq!(
+        micromark("[link](foo\\bar)"),
+        "<p><a href=\"foo%5Cbar\">link</a></p>",
+        "should not support non-punctuation character escapes in links"
+    );
+
+    assert_eq!(
+        micromark("[link](foo%20b&auml;)"),
+        "<p><a href=\"foo%20b%C3%A4\">link</a></p>",
+        "should support character references in links"
+    );
+
+    assert_eq!(
+        micromark("[link](\"title\")"),
+        "<p><a href=\"%22title%22\">link</a></p>",
+        "should not support links w/ only a title"
+    );
+
+    assert_eq!(
+        micromark("[link](/url \"title\")"),
+        "<p><a href=\"/url\" title=\"title\">link</a></p>",
+        "should support titles w/ double quotes"
+    );
+
+    assert_eq!(
+        micromark("[link](/url 'title')"),
+        "<p><a href=\"/url\" title=\"title\">link</a></p>",
+        "should support titles w/ single quotes"
+    );
+
+    assert_eq!(
+        micromark("[link](/url (title))"),
+        "<p><a href=\"/url\" title=\"title\">link</a></p>",
+        "should support titles w/ parens"
+    );
+
+    assert_eq!(
+        micromark("[link](/url \"title \\\"&quot;\")"),
+        "<p><a href=\"/url\" title=\"title &quot;&quot;\">link</a></p>",
+        "should support character references and escapes in titles"
+    );
+
+    assert_eq!(
+        micromark("[link](/url \"title\")"),
+        "<p><a href=\"/url%C2%A0%22title%22\">link</a></p>",
+        "should not support unicode whitespace between destination and title"
+    );
+
+    assert_eq!(
+        micromark("[link](/url \"title \"and\" title\")"),
+        "<p>[link](/url &quot;title &quot;and&quot; title&quot;)</p>",
+        "should not support nested balanced quotes in title"
+    );
+
+    assert_eq!(
+        micromark("[link](/url 'title \"and\" title')"),
+        "<p><a href=\"/url\" title=\"title &quot;and&quot; title\">link</a></p>",
+        "should support the other quotes in titles"
+    );
+
+    assert_eq!(
+        micromark("[link](   /uri\n  \"title\"  )"),
+        "<p><a href=\"/uri\" title=\"title\">link</a></p>",
+        "should support whitespace around destination and title (1)"
+    );
+
+    assert_eq!(
+        micromark("[link](\t\n/uri \"title\")"),
+        "<p><a href=\"/uri\" title=\"title\">link</a></p>",
+        "should support whitespace around destination and title (2)"
+    );
+
+    assert_eq!(
+        micromark("[link](/uri  \"title\"\t\n)"),
+        "<p><a href=\"/uri\" title=\"title\">link</a></p>",
+        "should support whitespace around destination and title (3)"
+    );
+
+    assert_eq!(
+        micromark("[link] (/uri)"),
+        "<p>[link] (/uri)</p>",
+        "should not support whitespace between label and resource"
+    );
+
+    assert_eq!(
+        micromark("[link [foo [bar]]](/uri)"),
+        "<p><a href=\"/uri\">link [foo [bar]]</a></p>",
+        "should support balanced brackets"
+    );
+
+    assert_eq!(
+        micromark("[link] bar](/uri)"),
+        "<p>[link] bar](/uri)</p>",
+        "should not support unbalanced brackets (1)"
+    );
+
+    assert_eq!(
+        micromark("[link [bar](/uri)"),
+        "<p>[link <a href=\"/uri\">bar</a></p>",
+        "should not support unbalanced brackets (2)"
+    );
+
+    assert_eq!(
+        micromark("[link \\[bar](/uri)"),
+        "<p><a href=\"/uri\">link [bar</a></p>",
+        "should support characer escapes"
+    );
+
+    // To do: attention.
+    // assert_eq!(
+    //     micromark("[link *foo **bar** `#`*](/uri)"),
+    //     "<p><a href=\"/uri\">link <em>foo <strong>bar</strong> <code>#</code></em></a></p>",
+    //     "should support content"
+    // );
+
+    assert_eq!(
+        micromark("[![moon](moon.jpg)](/uri)"),
+        "<p><a href=\"/uri\"><img src=\"moon.jpg\" alt=\"moon\" /></a></p>",
+        "should support an image as content"
+    );
+
+    assert_eq!(
+        micromark("[foo [bar](/uri)](/uri)"),
+        "<p>[foo <a href=\"/uri\">bar</a>](/uri)</p>",
+        "should not support links in links (1)"
+    );
+
+    // To do: attention.
+    // assert_eq!(
+    //     micromark("[foo *[bar [baz](/uri)](/uri)*](/uri)"),
+    //     "<p>[foo <em>[bar <a href=\"/uri\">baz</a>](/uri)</em>](/uri)</p>",
+    //     "should not support links in links (2)"
+    // );
+
+    // To do: tags in images.
+    // assert_eq!(
+    //     micromark("![[[foo](uri1)](uri2)](uri3)"),
+    //     "<p><img src=\"uri3\" alt=\"[foo](uri2)\" /></p>",
+    //     "should not support links in links (3)"
+    // );
+
+    assert_eq!(
+        micromark("*[foo*](/uri)"),
+        "<p>*<a href=\"/uri\">foo*</a></p>",
+        "should prefer links over emphasis (1)"
+    );
+
+    assert_eq!(
+        micromark("[foo *bar](baz*)"),
+        "<p><a href=\"baz*\">foo *bar</a></p>",
+        "should prefer links over emphasis (2)"
+    );
+
+    assert_eq!(
+        micromark_with_options("[foo <bar attr=\"](baz)\">", DANGER),
+        "<p>[foo <bar attr=\"](baz)\"></p>",
+        "should prefer HTML over links"
+    );
+
+    assert_eq!(
+        micromark("[foo`](/uri)`"),
+        "<p>[foo<code>](/uri)</code></p>",
+        "should prefer code over links"
+    );
+
+    assert_eq!(
+        micromark("[foo<http://example.com/?search=](uri)>"),
+        "<p>[foo<a href=\"http://example.com/?search=%5D(uri)\">http://example.com/?search=](uri)</a></p>",
+        "should prefer autolinks over links"
+    );
+
+    assert_eq!(
+        micromark("[foo<http://example.com/?search=](uri)>"),
+        "<p>[foo<a href=\"http://example.com/?search=%5D(uri)\">http://example.com/?search=](uri)</a></p>",
+        "should prefer autolinks over links"
+    );
+
+    // Extra
+    assert_eq!(
+        micromark("[]()"),
+        "<p><a href=\"\"></a></p>",
+        "should support an empty link"
+    );
+
+    // See: <https://github.com/commonmark/commonmark.js/issues/192>
+    assert_eq!(
+        micromark("[](<> \"\")"),
+        "<p><a href=\"\"></a></p>",
+        "should ignore an empty title"
+    );
+
+    assert_eq!(
+        micromark_with_options("[a](<b>\"c\")", DANGER),
+        "<p>[a](<b>&quot;c&quot;)</p>",
+        "should require whitespace between enclosed destination and title"
+    );
+
+    assert_eq!(
+        micromark("[](<"),
+        "<p>[](&lt;</p>",
+        "should not support an unclosed enclosed destination"
+    );
+
+    assert_eq!(
+        micromark("[]("),
+        "<p>[](</p>",
+        "should not support an unclosed destination"
+    );
+
+    assert_eq!(
+        micromark("[](\\<)"),
+        "<p><a href=\"%3C\"></a></p>",
+        "should support unenclosed link destination starting w/ escapes"
+    );
+
+    assert_eq!(
+        micromark("[](<\\<>)"),
+        "<p><a href=\"%3C\"></a></p>",
+        "should support enclosed link destination starting w/ escapes"
+    );
+
+    assert_eq!(
+        micromark("[](\\"),
+        "<p>[](\\</p>",
+        "should not support unenclosed link destination starting w/ an incorrect escape"
+    );
+
+    assert_eq!(
+        micromark("[](<\\"),
+        "<p>[](&lt;\\</p>",
+        "should not support enclosed link destination starting w/ an incorrect escape"
+    );
+
+    assert_eq!(
+        micromark("[](a \""),
+        "<p>[](a &quot;</p>",
+        "should not support an eof in a link title (1)"
+    );
+
+    assert_eq!(
+        micromark("[](a '"),
+        "<p>[](a '</p>",
+        "should not support an eof in a link title (2)"
+    );
+
+    assert_eq!(
+        micromark("[](a ("),
+        "<p>[](a (</p>",
+        "should not support an eof in a link title (3)"
+    );
+
+    assert_eq!(
+        micromark("[](a \"\\"),
+        "<p>[](a &quot;\\</p>",
+        "should not support an eof in a link title escape (1)"
+    );
+
+    assert_eq!(
+        micromark("[](a '\\"),
+        "<p>[](a '\\</p>",
+        "should not support an eof in a link title escape (2)"
+    );
+
+    assert_eq!(
+        micromark("[](a (\\"),
+        "<p>[](a (\\</p>",
+        "should not support an eof in a link title escape (3)"
+    );
+
+    assert_eq!(
+        micromark("[](a \"\\\"\")"),
+        "<p><a href=\"a\" title=\"&quot;\"></a></p>",
+        "should support a character escape to start a link title (1)"
+    );
+
+    assert_eq!(
+        micromark("[](a '\\'')"),
+        "<p><a href=\"a\" title=\"\'\"></a></p>",
+        "should support a character escape to start a link title (2)"
+    );
+
+    assert_eq!(
+        micromark("[](a (\\)))"),
+        "<p><a href=\"a\" title=\")\"></a></p>",
+        "should support a character escape to start a link title (3)"
+    );
+
+    assert_eq!(
+        micromark("[&amp;&copy;&](example.com/&amp;&copy;& \"&amp;&copy;&\")"),
+        "<p><a href=\"example.com/&amp;%C2%A9&amp;\" title=\"&amp;©&amp;\">&amp;©&amp;</a></p>",
+        "should support character references in links"
+    );
+
+    assert_eq!(
+        micromark("[a](1())"),
+        "<p><a href=\"1()\">a</a></p>",
+        "should support 1 set of parens"
+    );
+
+    assert_eq!(
+        micromark("[a](1(2()))"),
+        "<p><a href=\"1(2())\">a</a></p>",
+        "should support 2 sets of parens"
+    );
+
+    assert_eq!(
+        micromark(
+            "[a](1(2(3(4(5(6(7(8(9(10(11(12(13(14(15(16(17(18(19(20(21(22(23(24(25(26(27(28(29(30(31(32()))))))))))))))))))))))))))))))))"
+        ),
+        "<p><a href=\"1(2(3(4(5(6(7(8(9(10(11(12(13(14(15(16(17(18(19(20(21(22(23(24(25(26(27(28(29(30(31(32())))))))))))))))))))))))))))))))\">a</a></p>",
+        "should support 32 sets of parens"
+    );
+
+    assert_eq!(
+        micromark(
+            "[a](1(2(3(4(5(6(7(8(9(10(11(12(13(14(15(16(17(18(19(20(21(22(23(24(25(26(27(28(29(30(31(32(33())))))))))))))))))))))))))))))))))"
+        ),
+        "<p>[a](1(2(3(4(5(6(7(8(9(10(11(12(13(14(15(16(17(18(19(20(21(22(23(24(25(26(27(28(29(30(31(32(33())))))))))))))))))))))))))))))))))</p>",
+        "should not support 33 or more sets of parens"
+    );
+
+    assert_eq!(
+        micromark("[a](b \"\n c\")"),
+        "<p><a href=\"b\" title=\"\nc\">a</a></p>",
+        "should support an eol at the start of a title"
+    );
+
+    assert_eq!(
+        micromark("[a](b( \"c\")"),
+        "<p>[a](b( &quot;c&quot;)</p>",
+        "should not support whitespace when unbalanced in a raw destination"
+    );
+
+    assert_eq!(
+        micromark("[a](\0)"),
+        "<p><a href=\"%EF%BF%BD\">a</a></p>",
+        "should support a single NUL character as a link resource"
+    );
+}
diff --git a/tests/misc_dangerous_protocol.rs b/tests/misc_dangerous_protocol.rs
index 6f759e3..3aa042a 100644
--- a/tests/misc_dangerous_protocol.rs
+++ b/tests/misc_dangerous_protocol.rs
@@ -34,166 +34,164 @@ fn dangerous_protocol_autolink() {
     );
 }
 
-// To do: image.
-// #[test]
-// fn dangerous_protocol_image() {
-//     assert_eq!(
-//         micromark("![](javascript:alert(1))"),
-//         "<p><img src=\"\" alt=\"\" /></p>",
-//         "should be safe by default"
-//     );
-
-//     assert_eq!(
-//         micromark("![](http://a)"),
-//         "<p><img src=\"http://a\" alt=\"\" /></p>",
-//         "should allow `http:`"
-//     );
-
-//     assert_eq!(
-//         micromark("![](https://a)"),
-//         "<p><img src=\"https://a\" alt=\"\" /></p>",
-//         "should allow `https:`"
-//     );
-
-//     assert_eq!(
-//         micromark("![](irc:///help)"),
-//         "<p><img src=\"\" alt=\"\" /></p>",
-//         "should not allow `irc:`"
-//     );
-
-//     assert_eq!(
-//         micromark("![](mailto:a)"),
-//         "<p><img src=\"\" alt=\"\" /></p>",
-//         "should not allow `mailto:`"
-//     );
-
-//     assert_eq!(
-//         micromark("![](#a)"),
-//         "<p><img src=\"#a\" alt=\"\" /></p>",
-//         "should allow a hash"
-//     );
-
-//     assert_eq!(
-//         micromark("![](?a)"),
-//         "<p><img src=\"?a\" alt=\"\" /></p>",
-//         "should allow a search"
-//     );
-
-//     assert_eq!(
-//         micromark("![](/a)"),
-//         "<p><img src=\"/a\" alt=\"\" /></p>",
-//         "should allow an absolute"
-//     );
-
-//     assert_eq!(
-//         micromark("![](./a)"),
-//         "<p><img src=\"./a\" alt=\"\" /></p>",
-//         "should allow an relative"
-//     );
-
-//     assert_eq!(
-//         micromark("![](../a)"),
-//         "<p><img src=\"../a\" alt=\"\" /></p>",
-//         "should allow an upwards relative"
-//     );
-
-//     assert_eq!(
-//         micromark("![](a#b:c)"),
-//         "<p><img src=\"a#b:c\" alt=\"\" /></p>",
-//         "should allow a colon in a hash"
-//     );
-
-//     assert_eq!(
-//         micromark("![](a?b:c)"),
-//         "<p><img src=\"a?b:c\" alt=\"\" /></p>",
-//         "should allow a colon in a search"
-//     );
-
-//     assert_eq!(
-//         micromark("![](a/b:c)"),
-//         "<p><img src=\"a/b:c\" alt=\"\" /></p>",
-//         "should allow a colon in a path"
-//     );
-// }
-
-// To do: link.
-// #[test]
-// fn dangerous_protocol_link() {
-//     assert_eq!(
-//         micromark("[](javascript:alert(1))"),
-//         "<p><a href=\"\"></a></p>",
-//         "should be safe by default"
-//     );
-
-//     assert_eq!(
-//         micromark("[](http://a)"),
-//         "<p><a href=\"http://a\"></a></p>",
-//         "should allow `http:`"
-//     );
-
-//     assert_eq!(
-//         micromark("[](https://a)"),
-//         "<p><a href=\"https://a\"></a></p>",
-//         "should allow `https:`"
-//     );
-
-//     assert_eq!(
-//         micromark("[](irc:///help)"),
-//         "<p><a href=\"irc:///help\"></a></p>",
-//         "should allow `irc:`"
-//     );
-
-//     assert_eq!(
-//         micromark("[](mailto:a)"),
-//         "<p><a href=\"mailto:a\"></a></p>",
-//         "should allow `mailto:`"
-//     );
-
-//     assert_eq!(
-//         micromark("[](#a)"),
-//         "<p><a href=\"#a\"></a></p>",
-//         "should allow a hash"
-//     );
-
-//     assert_eq!(
-//         micromark("[](?a)"),
-//         "<p><a href=\"?a\"></a></p>",
-//         "should allow a search"
-//     );
-
-//     assert_eq!(
-//         micromark("[](/a)"),
-//         "<p><a href=\"/a\"></a></p>",
-//         "should allow an absolute"
-//     );
-
-//     assert_eq!(
-//         micromark("[](./a)"),
-//         "<p><a href=\"./a\"></a></p>",
-//         "should allow an relative"
-//     );
-
-//     assert_eq!(
-//         micromark("[](../a)"),
-//         "<p><a href=\"../a\"></a></p>",
-//         "should allow an upwards relative"
-//     );
-
-//     assert_eq!(
-//         micromark("[](a#b:c)"),
-//         "<p><a href=\"a#b:c\"></a></p>",
-//         "should allow a colon in a hash"
-//     );
-
-//     assert_eq!(
-//         micromark("[](a?b:c)"),
-//         "<p><a href=\"a?b:c\"></a></p>",
-//         "should allow a colon in a search"
-//     );
-
-//     assert_eq!(
-//         micromark("[](a/b:c)"),
-//         "<p><a href=\"a/b:c\"></a></p>",
-//         "should allow a colon in a path"
-//     );
-// }
+#[test]
+fn dangerous_protocol_image() {
+    assert_eq!(
+        micromark("![](javascript:alert(1))"),
+        "<p><img src=\"\" alt=\"\" /></p>",
+        "should be safe by default"
+    );
+
+    assert_eq!(
+        micromark("![](http://a)"),
+        "<p><img src=\"http://a\" alt=\"\" /></p>",
+        "should allow `http:`"
+    );
+
+    assert_eq!(
+        micromark("![](https://a)"),
+        "<p><img src=\"https://a\" alt=\"\" /></p>",
+        "should allow `https:`"
+    );
+
+    assert_eq!(
+        micromark("![](irc:///help)"),
+        "<p><img src=\"\" alt=\"\" /></p>",
+        "should not allow `irc:`"
+    );
+
+    assert_eq!(
+        micromark("![](mailto:a)"),
+        "<p><img src=\"\" alt=\"\" /></p>",
+        "should not allow `mailto:`"
+    );
+
+    assert_eq!(
+        micromark("![](#a)"),
+        "<p><img src=\"#a\" alt=\"\" /></p>",
+        "should allow a hash"
+    );
+
+    assert_eq!(
+        micromark("![](?a)"),
+        "<p><img src=\"?a\" alt=\"\" /></p>",
+        "should allow a search"
+    );
+
+    assert_eq!(
+        micromark("![](/a)"),
+        "<p><img src=\"/a\" alt=\"\" /></p>",
+        "should allow an absolute"
+    );
+
+    assert_eq!(
+        micromark("![](./a)"),
+        "<p><img src=\"./a\" alt=\"\" /></p>",
+        "should allow an relative"
+    );
+
+    assert_eq!(
+        micromark("![](../a)"),
+        "<p><img src=\"../a\" alt=\"\" /></p>",
+        "should allow an upwards relative"
+    );
+
+    assert_eq!(
+        micromark("![](a#b:c)"),
+        "<p><img src=\"a#b:c\" alt=\"\" /></p>",
+        "should allow a colon in a hash"
+    );
+
+    assert_eq!(
+        micromark("![](a?b:c)"),
+        "<p><img src=\"a?b:c\" alt=\"\" /></p>",
+        "should allow a colon in a search"
+    );
+
+    assert_eq!(
+        micromark("![](a/b:c)"),
+        "<p><img src=\"a/b:c\" alt=\"\" /></p>",
+        "should allow a colon in a path"
+    );
+}
+
+#[test]
+fn dangerous_protocol_link() {
+    assert_eq!(
+        micromark("[](javascript:alert(1))"),
+        "<p><a href=\"\"></a></p>",
+        "should be safe by default"
+    );
+
+    assert_eq!(
+        micromark("[](http://a)"),
+        "<p><a href=\"http://a\"></a></p>",
+        "should allow `http:`"
+    );
+
+    assert_eq!(
+        micromark("[](https://a)"),
+        "<p><a href=\"https://a\"></a></p>",
+        "should allow `https:`"
+    );
+
+    assert_eq!(
+        micromark("[](irc:///help)"),
+        "<p><a href=\"irc:///help\"></a></p>",
+        "should allow `irc:`"
+    );
+
+    assert_eq!(
+        micromark("[](mailto:a)"),
+        "<p><a href=\"mailto:a\"></a></p>",
+        "should allow `mailto:`"
+    );
+
+    assert_eq!(
+        micromark("[](#a)"),
+        "<p><a href=\"#a\"></a></p>",
+        "should allow a hash"
+    );
+
+    assert_eq!(
+        micromark("[](?a)"),
+        "<p><a href=\"?a\"></a></p>",
+        "should allow a search"
+    );
+
+    assert_eq!(
+        micromark("[](/a)"),
+        "<p><a href=\"/a\"></a></p>",
+        "should allow an absolute"
+    );
+
+    assert_eq!(
+        micromark("[](./a)"),
+        "<p><a href=\"./a\"></a></p>",
+        "should allow an relative"
+    );
+
+    assert_eq!(
+        micromark("[](../a)"),
+        "<p><a href=\"../a\"></a></p>",
+        "should allow an upwards relative"
+    );
+
+    assert_eq!(
+        micromark("[](a#b:c)"),
+        "<p><a href=\"a#b:c\"></a></p>",
+        "should allow a colon in a hash"
+    );
+
+    assert_eq!(
+        micromark("[](a?b:c)"),
+        "<p><a href=\"a?b:c\"></a></p>",
+        "should allow a colon in a search"
+    );
+
+    assert_eq!(
+        micromark("[](a/b:c)"),
+        "<p><a href=\"a/b:c\"></a></p>",
+        "should allow a colon in a path"
+    );
+}
diff --git a/tests/misc_tabs.rs b/tests/misc_tabs.rs
index e9a0b72..568172e 100644
--- a/tests/misc_tabs.rs
+++ b/tests/misc_tabs.rs
@@ -221,48 +221,42 @@ fn tabs_text() {
     //     "should support an initial tab after a line ending in a paragraph"
     // );
 
-    // To do: link (reference).
-    // assert_eq!(
-    //     micromark("x[\ty](z)"),
-    //     "<p>x<a href=\"z\">\ty</a></p>",
-    //     "should support an initial tab in a link label"
-    // );
+    assert_eq!(
+        micromark("x[\ty](z)"),
+        "<p>x<a href=\"z\">\ty</a></p>",
+        "should support an initial tab in a link label"
+    );
 
-    // To do: link (reference).
-    // assert_eq!(
-    //     micromark("x[y\t](z)"),
-    //     "<p>x<a href=\"z\">y\t</a></p>",
-    //     "should support a final tab in a link label"
-    // );
+    assert_eq!(
+        micromark("x[y\t](z)"),
+        "<p>x<a href=\"z\">y\t</a></p>",
+        "should support a final tab in a link label"
+    );
 
-    // To do: link (reference).
-    // assert_eq!(
-    //     micromark("[x\ty](z)"),
-    //     "<p><a href=\"z\">x\ty</a></p>",
-    //     "should support a tab in a link label"
-    // );
+    assert_eq!(
+        micromark("[x\ty](z)"),
+        "<p><a href=\"z\">x\ty</a></p>",
+        "should support a tab in a link label"
+    );
 
-    // To do: link (resource).
     // Note: CM.js bug, see: <https://github.com/commonmark/commonmark.js/issues/191>
-    // assert_eq!(
-    //     micromark("[x](\ty)"),
-    //     "<p><a href=\"y\">x</a></p>",
-    //     "should support a tab starting a link resource"
-    // );
+    assert_eq!(
+        micromark("[x](\ty)"),
+        "<p><a href=\"y\">x</a></p>",
+        "should support a tab starting a link resource"
+    );
 
-    // To do: link (resource).
-    // assert_eq!(
-    //     micromark("[x](y\t)"),
-    //     "<p><a href=\"y\">x</a></p>",
-    //     "should support a tab ending a link resource"
-    // );
+    assert_eq!(
+        micromark("[x](y\t)"),
+        "<p><a href=\"y\">x</a></p>",
+        "should support a tab ending a link resource"
+    );
 
-    // To do: link (resource).
-    // assert_eq!(
-    //     micromark("[x](y\t\"z\")"),
-    //     "<p><a href=\"y\" title=\"z\">x</a></p>",
-    //     "should support a tab between a link destination and title"
-    // );
+    assert_eq!(
+        micromark("[x](y\t\"z\")"),
+        "<p><a href=\"y\" title=\"z\">x</a></p>",
+        "should support a tab between a link destination and title"
+    );
 }
 
 #[test]
diff --git a/tests/misc_url.rs b/tests/misc_url.rs
index a6f8ead..5e94366 100644
--- a/tests/misc_url.rs
+++ b/tests/misc_url.rs
@@ -9,28 +9,25 @@ fn url() {
         "should support incorrect percentage encoded values (0)"
     );
 
-    // To do: link.
-    // assert_eq!(
-    //     micromark("[](<%>)"),
-    //     "<p><a href=\"%25\"></a></p>",
-    //     "should support incorrect percentage encoded values (1)"
-    // );
-
-    // To do: link.
-    // assert_eq!(
-    //     micromark("[](<%%20>)"),
-    //     "<p><a href=\"%25%20\"></a></p>",
-    //     "should support incorrect percentage encoded values (2)"
-    // );
-
-    // To do: link.
-    // assert_eq!(
-    //     micromark("[](<%a%20>)"),
-    //     "<p><a href=\"%25a%20\"></a></p>",
-    //     "should support incorrect percentage encoded values (3)"
-    // );
+    assert_eq!(
+        micromark("[](<%>)"),
+        "<p><a href=\"%25\"></a></p>",
+        "should support incorrect percentage encoded values (1)"
+    );
 
-    // Surrogate handling not needed in Rust.
+    assert_eq!(
+        micromark("[](<%%20>)"),
+        "<p><a href=\"%25%20\"></a></p>",
+        "should support incorrect percentage encoded values (2)"
+    );
+
+    assert_eq!(
+        micromark("[](<%a%20>)"),
+        "<p><a href=\"%25a%20\"></a></p>",
+        "should support incorrect percentage encoded values (3)"
+    );
+
+    // Note: Surrogate handling not needed in Rust.
     //   assert_eq!(
     //     micromark("[](<foo\u{D800}bar>)"),
     //     "<p><a href=\"foo%EF%BF%BDbar\"></a></p>",
@@ -114,39 +111,37 @@ fn url() {
     //     "should support a lone low surrogate at the end (highest)"
     //   );
 
-    // To do: link.
-    // assert_eq!(
-    //     micromark("[](<🤔>)"),
-    //     "<p><a href=\"%F0%9F%A4%94\"></a></p>",
-    //     "should support an emoji"
-    // );
-
-    // To do: link.
-    // let mut ascii: Vec<char> = vec![];
-    // let mut code = 0;
-
-    // while code < 128 {
-    //     // LF and CR can’t be in resources.
-    //     if code == 10 || code == 13 {
-    //         code += 1;
-    //         continue;
-    //     }
-
-    //     // `<`, `>`, `\` need to be escaped.
-    //     if code == 60 || code == 62 || code == 92 {
-    //         ascii.push('\\');
-    //     }
-
-    //     ascii.push(char::from_u32(code).unwrap());
-
-    //     code += 1;
-    // }
-
-    // let ascii_in = ascii.into_iter().collect::<String>();
-    // let ascii_out = "%EF%BF%BD%01%02%03%04%05%06%07%08%09%0B%0C%0E%0F%10%11%12%13%14%15%16%17%18%19%1A%1B%1C%1D%1E%1F%20!%22#$%25&amp;\"()*+,-./0123456789:;%3C=%3E?@ABCDEFGHIJKLMNOPQRSTUVWXYZ%5B%5C%5D%5E_%60abcdefghijklmnopqrstuvwxyz%7B%7C%7D~%7F";
-    // assert_eq!(
-    //     micromark(&format!("[](<{}>)", ascii_in)),
-    //     format!("<p><a href=\"{}\"></a></p>", ascii_out),
-    //     "should support ascii characters"
-    // );
+    assert_eq!(
+        micromark("[](<🤔>)"),
+        "<p><a href=\"%F0%9F%A4%94\"></a></p>",
+        "should support an emoji"
+    );
+
+    let mut ascii: Vec<char> = vec![];
+    let mut code = 0;
+
+    while code < 128 {
+        // LF and CR can’t be in resources.
+        if code == 10 || code == 13 {
+            code += 1;
+            continue;
+        }
+
+        // `<`, `>`, `\` need to be escaped.
+        if code == 60 || code == 62 || code == 92 {
+            ascii.push('\\');
+        }
+
+        ascii.push(char::from_u32(code).unwrap());
+
+        code += 1;
+    }
+
+    let ascii_in = ascii.into_iter().collect::<String>();
+    let ascii_out = "%EF%BF%BD%01%02%03%04%05%06%07%08%09%0B%0C%0E%0F%10%11%12%13%14%15%16%17%18%19%1A%1B%1C%1D%1E%1F%20!%22#$%25&amp;'()*+,-./0123456789:;%3C=%3E?@ABCDEFGHIJKLMNOPQRSTUVWXYZ%5B%5C%5D%5E_%60abcdefghijklmnopqrstuvwxyz%7B%7C%7D~%7F";
+    assert_eq!(
+        micromark(&format!("[](<{}>)", ascii_in)),
+        format!("<p><a href=\"{}\"></a></p>", ascii_out),
+        "should support ascii characters"
+    );
 }