HTML Guide for illegal character
The pipe character | is not permitted in the query component of a URL in the href attribute of an a element.
According to the WHATWG and W3C HTML specifications, URLs in attributes such as href must be valid and properly encoded. The pipe character | is not a valid character in the query string of a URL unless it is percent-encoded as %7C. Failing to encode it will cause validation errors. This is especially important for interoperability and security across browsers and user agents.
Incorrect example (invalid href with pipe):
<a href="https://example.com/search?q=test|demo">Invalid link</a>Correct example (pipe character encoded):
<a href="https://example.com/search?q=test%7Cdemo">Valid link</a>Always encode special characters such as | in URLs used within HTML attributes to ensure your documents validate and behave consistently.
The href attribute on an element <a> contains a character that is not allowed, and should be encoded.
Some typical examples include the pipe character | that should be replaced by its encoded alternative %7C , and the left square bracket [ that needs to be encoded as %5B.
A tab character has been found in the domain part for an href attribute, which is not allowed.
The href attribute on an element <link> contains a character that is not allowed, and should be encoded.
Some typical examples include the pipe character | that should be replaced by its encoded alternative %7C , and the left square bracket [ that needs to be encoded as %5B.
The src attribute on an element <img> contains a character that is not allowed, and should be encoded.
Some typical examples include the pipe character | that should be replaced by its encoded alternative %7C , and the left square bracket [ that needs to be encoded as %5B.