debugCSS is meant to be loaded on an existing page to highlight potentially broken, malformed or legacy (X)HTML.

Not all "errors" are created equally, so they are color coded to highlight severity. Green is "probably not a big problem", yellow is "worth looking at" and red is "you really should fix this."

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debugCSS

Get the source code on GitHub : imbrianj/debugCSS

• a a

  Note: this test may always pass as most browsers seem to move the anchor out from within the other.

  Nested Anchors

• img:not([src])

• img[src=""]

• img[src="#"]

  

• h1 div

  Div within header

  Note: Similarly, h2 - h6 are applicable

• a div

  Block level element within anchor

• span div

  Block level element within anchor

• html[xmlns] a h1

  Block level element within anchor

  Note: Similarly, h2 - h6 are applicable. Not applicable for HTML5, so filtering for XHTML.

• ol > *:not(li)

  Header does not belong here

  1. List
  2. Item

• ul > *:not(li)

  Header does not belong here

  1. List
  2. Item

• dl > *:not(dt):not(dd)

  Header does not belong here

  Term

  Definition

• center

  Deprecated tag

• u

  Deprecated tag

• font

  Deprecated tag

• map

• br

  Possibly an unnecessary use of
  a line break

• br br

  Text trying to
  
  be a paragraph

• b

  Deprecated tag

• i

  Deprecated tag

• blink

  Deprecated tag

• marquee

  Deprecated tag
• Script tag without type
• Style tag without type

• *[width]

  Width should be specified in CSS

  Note: This is allowable in transitional doctypes

• *[height]

  Height should be specified in CSS

  Note: This is allowable in transitional doctypes

• *[border]

  Border should be specified in CSS

  Note: This is allowable in transitional doctypes

• body script ~ *:not(script)

  Script not the last element in the body

• body style

  Style inside body

• *[style="[object Object]"]

  Style wrongly applied via JS