1 files changed, 56 insertions, 0 deletions
diff --git a/src/construct/partial_whitespace.rs b/src/construct/partial_whitespace.rs
new file mode 100644
index 0000000..9a7a54d
--- /dev/null
+++ b/src/construct/partial_whitespace.rs
@@ -0,0 +1,56 @@
+//! Trailing whitespace occurs in [string][] and [text][].
+//!
+//! It occurs at the start or end of the whole, or around line endings.
+//! This whitespace is ignored
+//!
+//! They’re formed with the following BNF:
+//!
+//! ```bnf
+//! ; Restriction: the start and end here count as an eol.
+//! whitespace ::= 0.*space_or_tab eol 0.*space_or_tab
+//! ```
+//!
+//! ## References
+//!
+//! *   [`initialize/text.js` in `micromark`](https://github.com/micromark/micromark/blob/main/packages/micromark/dev/lib/initialize/text.js)
+//!
+//! [string]: crate::content::string
+//! [text]: crate::content::text
+
+use super::partial_space_or_tab::space_or_tab;
+use crate::tokenizer::{Code, State, StateFnResult, Tokenizer};
+
+/// Parse initial or final whitespace.
+pub fn whitespace(tokenizer: &mut Tokenizer, code: Code) -> StateFnResult {
+    tokenizer.go(
+        // Nothing if there’s no whitespace.
+        space_or_tab(),
+        if matches!(
+            tokenizer.previous,
+            Code::None | Code::CarriageReturnLineFeed | Code::Char('\r' | '\n')
+        ) {
+            // If there’s whitespace, and we were at an eol/eof, `ok`
+            ok
+        } else {
+            // If there’s whitespace, and we were not at an eol/eof, there must be one here.
+            at_eol
+        },
+    )(tokenizer, code)
+}
+
+/// After whitespace, at an eol/eof.
+fn at_eol(tokenizer: &mut Tokenizer, code: Code) -> StateFnResult {
+    if matches!(
+        code,
+        Code::None | Code::CarriageReturnLineFeed | Code::Char('\r' | '\n')
+    ) {
+        ok(tokenizer, code)
+    } else {
+        (State::Nok, None)
+    }
+}
+
+/// Fine.
+fn ok(_tokenizer: &mut Tokenizer, code: Code) -> StateFnResult {
+    (State::Ok, Some(vec![code]))
+}