anil.recoil.org
OCaml HTML5 parser/serialiser based on Python's JustHTML
1(*---------------------------------------------------------------------------
2 Copyright (c) 2025 Anil Madhavapeddy <anil@recoil.org>. All rights reserved.
3 SPDX-License-Identifier: MIT
4 ---------------------------------------------------------------------------*)
5
6(** Srcset and sizes attribute validation checker.
7
8 This checker validates the [srcset] and [sizes] attributes on [<img>]
9 and [<source>] elements. These attributes use a specialized microsyntax
10 for responsive images.
11
12 {2 Srcset Syntax}
13
14 The [srcset] attribute contains a comma-separated list of image
15 candidates, each with:
16 - A URL
17 - An optional width descriptor ([Nw], e.g., "800w")
18 - Or an optional pixel density descriptor ([Nx], e.g., "2x")
19
20 Width and pixel density descriptors cannot be mixed in the same srcset.
21
22 {2 Sizes Syntax}
23
24 The [sizes] attribute contains a comma-separated list of:
25 - Media conditions (optional)
26 - Source sizes (CSS lengths)
27
28 The last entry should not have a media condition (it's the default).
29
30 {2 Validation Rules}
31
32 - URLs in srcset must be valid
33 - Width descriptors must be positive integers
34 - Pixel density descriptors must be positive numbers
35 - Sizes must use valid CSS length units
36 - Duplicate descriptors are flagged
37
38 {2 Error Messages}
39
40 - Invalid srcset syntax
41 - Invalid sizes syntax
42 - Missing sizes when srcset uses width descriptors
43 - Invalid CSS length units
44
45 @see <https://html.spec.whatwg.org/multipage/images.html#srcset-attributes>
46 HTML Standard: Srcset attributes
47*)
48
49val checker : Checker.t
50(** The srcset/sizes attribute checker instance. *)