Add docs for label start (image, link)

1 files changed, 30 insertions, 1 deletions

diff --git a/src/construct/label_start_image.rs b/src/construct/label_start_image.rs
index 2e96977..97231e0 100644
--- a/src/construct/label_start_image.rs
+++ b/src/construct/label_start_image.rs
@@ -1,4 +1,33 @@
-//! To do
+//! Label start (image) is a construct that occurs in the [text][] content
+//! type.
+//!
+//! It forms with the following BNF:
+//!
+//! ```bnf
+//! label_start_image ::= '!' '['
+//! ```
+//!
+//! Label start (images) relates to the `<img>` element in HTML.
+//! See [*§ 4.8.3 The `img` element*][html-img] in the HTML spec for more info.
+//!
+//! Whether it contributes an image depends on whether it is followed by a
+//! valid [label end][label_end] or not.
+//! Without an end, the characters (`![`) are output.
+//!
+//! ## Tokens
+//!
+//! *   [`LabelImage`][TokenType::LabelImage]
+//! *   [`LabelImageMarker`][TokenType::LabelImageMarker]
+//! *   [`LabelMarker`][TokenType::LabelMarker]
+//!
+//! ## References
+//!
+//! *   [`label-start-image.js` in `micromark`](https://github.com/micromark/micromark/blob/main/packages/micromark-core-commonmark/dev/lib/label-start-image.js)
+//! *   [*§ 6.4 Images* in `CommonMark`](https://spec.commonmark.org/0.30/#images)
+//!
+//! [text]: crate::content::text
+//! [label_end]: crate::construct::label_end
+//! [html-img]: https://html.spec.whatwg.org/multipage/embedded-content.html#the-img-element
 
 use super::label_end::resolve_media;
 use crate::tokenizer::{Code, LabelStart, State, StateFnResult, TokenType, Tokenizer};