HTML Checking for Large Sites

In order to define the charset encoding of an HTML document, both of these options are valid, but only one of them must appear in the document:

<!-- This is the preferred way -->
<meta charset="UTF-8">

<!-- This is the older way, also valid -->
<meta http-equiv="content-type" content="text/html; charset=UTF-8">

Read about specifying the character encoding

A <meta> tag has been found in the document stating that the charset is windows-1251, but it actually is utf-8. You should update the tag to reflect the actual encoding of the document, for example:

<meta http-equiv="Content-Type" content="text/html; charset=utf-8">

A <meta> tag has been found in the document stating that the charset is windows-1252, but it actually is utf-8. You should update the tag to reflect the actual encoding of the document, for example:

<meta http-equiv="Content-Type" content="text/html; charset=utf-8">

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/?s=some term">invalid</a>
<a href="https://example.com/?s=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.

The document has been declared to use a windows-1251 charset but the actual contents seems to be utf-8. You should update the charset to that like in this example:

<meta http-equiv="Content-Type" content="text/html; charset=utf-8">

In HTML5 you’re encouraged to use Unicode (UTF-8) character encoding rather than a legacy character encoding such as Latin1 (Windows-1252 or ISO 8859-1).

In short, it can be just a matter of using <meta charset="utf-8"/> in your document, but you should also ensure that your pages are also saved and served as UTF-8.

• W3C: Changing an HTML page to Unicode

Read about Normalization in HTML and CSS.