HTML Guide for parse error

The media attribute on a <link> element specifies the media for which the linked resource is intended, using a valid media query. The value indicated is not a valid media query, which leads to a parse error.

Explanation

The media attribute is used to define what type of device the linked stylesheet should be applied to. Examples include common media types like screen, print, or all, as well as more complex media queries, such as (max-width: 600px) for responsive designs.

Correct Usage

1. Media Type Only:

   You can specify general media types such as screen, print, or all.

   <link rel="stylesheet" href="styles.css" media="screen">

2. Media Query:

   For more precise control, use a media query to target specific conditions.

   <link rel="stylesheet" href="styles.css" media="(max-width: 600px)">

sizes contains an invalid media condition; the value must be a comma-separated list of media conditions with corresponding slot sizes, ending with an optional fallback length.

Detailed explanation:

• The sizes attribute on img pairs a media condition with a slot size that represents the layout width of the image for that condition. Syntax: (<media-condition>) <length>[, ...], <length> where the last item can be a bare length fallback.
• A media condition uses the same grammar as CSS media queries. It must be valid CSS, e.g., (min-width: 600px) or (width <= 50rem) and (orientation: landscape). Each condition must be enclosed in parentheses unless using logical operators combining proper conditions.

Common parse errors:

• Missing parentheses: use (min-width: 600px), not min-width: 600px.
• Invalid units or tokens: use px, em, rem, vw, etc.; avoid % in media conditions.
• Missing slot size after a condition: (min-width: 600px) must be followed by a length like 600px.
• Using px only for slot size without units or using percentages: slot size must be a length like 300px, 50vw, not 300.
• Trailing comma or extra commas.
• Misusing comparison syntax: use modern range syntax like (600px <= width <= 1000px) or the traditional form (min-width: 600px) and (max-width: 1000px). Do not write (min-width <= 600px).
• Slot sizes must be lengths: px, em, rem, vw, vh, vmin, vmax, ch. Percentages are not allowed in sizes slot sizes.
• The srcset widths (w descriptors) must correspond to the intrinsic widths of the image candidates, e.g., 400w, 800w. The browser picks one based on sizes.

HTML examples:

• Correct usage with media conditions and fallback:

  <img
    src="image-800.jpg"
    srcset="image-400.jpg 400w, image-800.jpg 800w, image-1200.jpg 1200w"
    sizes="(min-width: 900px) 50vw, (min-width: 600px) 66vw, 100vw"
    alt="Decorative pattern">

• Using range syntax and avoiding common mistakes:

  <img
    src="hero-1600.jpg"
    srcset="hero-800.jpg 800w, hero-1200.jpg 1200w, hero-1600.jpg 1600w"
    sizes="(800px <= width < 1200px) 80vw, (width >= 1200px) 50vw, 100vw"
    alt="Hero banner">

• Minimal fixed example for a typical error (missing parentheses and slot size): Incorrect:

  <img src="pic-800.jpg" srcset="pic-400.jpg 400w, pic-800.jpg 800w" sizes="min-width: 600px, 100vw" alt="Sample">

  Correct:

  <img src="pic-800.jpg" srcset="pic-400.jpg 400w, pic-800.jpg 800w" sizes="(min-width: 600px) 50vw, 100vw" alt="Sample">

• Example avoiding invalid tokens and commas:

  <img
    src="avatar-256.png"
    srcset="avatar-128.png 128w, avatar-256.png 256w"
    sizes="(orientation: landscape) 30vw, 50vw"
    alt="User avatar">

sizes only accepts a valid media condition list (e.g., (min-width: 600px) 50vw, 100vw); malformed media conditions or missing length values trigger this parse error.

Detailed explanation

• Element: source in a picture or audio/video context. For responsive images, use attributes srcset, optional media, and optional sizes.
• Attribute: sizes applies only when srcset contains width descriptors (e.g., 320w, 640w). It is a comma-separated list of:
  • One or more media conditions followed by a length (e.g., (min-width: 800px) 50vw)
  • A final fallback length with no media condition (e.g., 100vw)

Common parse errors:

• Missing parentheses around conditions: min-width: 600px → (min-width: 600px)
• Using invalid units or tokens: 50 (needs a length like 50vw or 50rem)
• Missing length after a condition: (min-width: 800px)
• Trailing commas or malformed separators
• Using sizes while srcset uses pixel density descriptors (1x, 2x); sizes is ignored for x-descriptors and may confuse validators
• Valid media condition syntax mirrors CSS media queries without the @media keyword. Use logical operators and, or, not per CSS Media Queries spec, and ensure spaces and colons are correct.

HTML examples

• Correct responsive image with width descriptors and sizes

  <picture>
  <source
    type="image/webp"
    srcset="hero-480.webp 480w, hero-800.webp 800w, hero-1200.webp 1200w"
    sizes="(min-width: 1200px) 1200px, (min-width: 800px) 800px, 100vw">
  <img
    src="hero-800.jpg"
    srcset="hero-480.jpg 480w, hero-800.jpg 800w, hero-1200.jpg 1200w"
    sizes="(min-width: 1200px) 1200px, (min-width: 800px) 800px, 100vw"
    alt="Hero image">
  </picture>

• Using viewport width units for simpler sizing

  <img
  src="photo-640.jpg"
  srcset="photo-320.jpg 320w, photo-640.jpg 640w, photo-1024.jpg 1024w"
  sizes="(min-width: 900px) 50vw, 100vw"
  alt="Sample photo">

• Correct when using pixel density descriptors (omit sizes)

  <img
  src="avatar@1x.jpg"
  srcset="avatar@1x.jpg 1x, avatar@2x.jpg 2x"
  alt="User avatar">

Fixing common mistakes

• Add parentheses and a length:

  <img
  src="img-800.jpg"
  srcset="img-480.jpg 480w, img-800.jpg 800w"
  sizes="(min-width: 600px) 50vw, 100vw"
  alt="Example">

• Remove stray comma and ensure final fallback:

  <img
  src="banner-800.jpg"
  srcset="banner-400.jpg 400w, banner-800.jpg 800w"
  sizes="(min-width: 700px) 60vw, 100vw"
  alt="Banner">

• Minimal valid document example

  <!doctype html>
  <html lang="en">
  <head>
    <meta charset="utf-8">
    <title>Valid sizes Attribute</title>
  </head>
  <body>
    <img
      src="pic-800.jpg"
      srcset="pic-400.jpg 400w, pic-800.jpg 800w"
      sizes="(min-width: 600px) 50vw, 100vw"
      alt="Picture">
  </body>
  </html>

A CSS definition for background-image could not be understood by the parser. Check its definition to ensure that it’s well formed and that it contains an appropriate value.

CSS styles could not be parsed, check the indicated line to find what caused the parser to fail. Common causes are unclosed curly brackets or comments, missing semicolons or unexpected or empty properties.

A CSS definition for an X property could not be understood by the parser. Check it to ensure that it’s well formed and that it contains an appropriate value.