HTML Checking for Large Sites

Read about Normalization in HTML and CSS.

The href attribute of an <a> element contains an invalid character, that should be properly encoded as a URI percent-encoded character.

The src attribute on an <img> element contains an invalid character, that should be properly encoded as a URI percent-encoded character.

The accept attribute may be specified to provide browsers with a hint of what file types will be accepted on an <input> element. It expects a comma-separated list of allowed file types. Refer to the list of media types to check the accepted tokens. In this example, the first line is invalid while the second is valid:

<input name='file' type='file' accept='doc, docx, pdf' />

<input name='file' type='file' accept='text/doc, text/docx, application/pdf' />

Space characters are not allowed in href attributes. Instead, they should be converted to %20. In this example, the first line is invalid and the second is valid:

<a href="https://example.com#some term">invalid</a>
<a href="https://example.com#some%20term">valid</a>

The href attribute on an <a> tag contains an space, which is not allowed. Consider replacing space characters with “%20”.

Space characters are not allowed in src attributes. Instead, they should be converted to %20. In this example, the first line is invalid and the second is valid:

<img src="https://example.com/?s=some term" alt="description" />
<img src="https://example.com/?s=some%20term" alt="description" />

The src attribute on an <img> tag is not allowed to contain space characters. You should replace them with “%20“.

An HTML tag could not be parsed, most probably because of a typo.

A character has been found in the document that is not allowed in the charset encoding being used.