Add docs for label start (image, link)

1 files changed, 29 insertions, 1 deletions

diff --git a/src/construct/label_start_link.rs b/src/construct/label_start_link.rs
index 35c9dcd..677fb50 100644
--- a/src/construct/label_start_link.rs
+++ b/src/construct/label_start_link.rs
@@ -1,4 +1,32 @@
-//! To do
+//! Label start (link) is a construct that occurs in the [text][] content
+//! type.
+//!
+//! It forms with the following BNF:
+//!
+//! ```bnf
+//! label_start_link ::= '['
+//! ```
+//!
+//! Label start (link) relates to the `<a>` element in HTML.
+//! See [*§ 4.5.1 The `a` element*][html-a] in the HTML spec for more info.
+//!
+//! Whether it contributes a link depends on whether it is followed by a
+//! valid [label end][label_end] or not.
+//! Without an end, the characters (`[`) are output.
+//!
+//! ## Tokens
+//!
+//! *   [`LabelLink`][TokenType::LabelLink]
+//! *   [`LabelMarker`][TokenType::LabelMarker]
+//!
+//! ## References
+//!
+//! *   [`label-start-link.js` in `micromark`](https://github.com/micromark/micromark/blob/main/packages/micromark-core-commonmark/dev/lib/label-start-link.js)
+//! *   [*§ 6.3 Links* in `CommonMark`](https://spec.commonmark.org/0.30/#links)
+//!
+//! [text]: crate::content::text
+//! [label_end]: crate::construct::label_end
+//! [html-a]: https://html.spec.whatwg.org/multipage/text-level-semantics.html#the-a-element
 
 use super::label_end::resolve_media;
 use crate::tokenizer::{Code, LabelStart, State, StateFnResult, TokenType, Tokenizer};