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Find out what web pages on your sites are affected by HTML issues.

Bad value X for attribute “srcset” on element “source”: Bad image-candidate URL: X: Percentage ("%") is not followed by two hexadecimal digits.

URLs need to be encoded so that special characters area escaped, for example space characters need to be converted to “%20”. All special characters will therefore be converted to a percent sign followed by two hexadecimal characters, to be later decoded. In case a percentage sign (%) is found without being followed by two hexadecimal digits, a decoding error will be raised.

The most probable cause is an URL that contains a % that has not been properly encoded to %25 which is the code for the percent sign. For example:

<!-- This is invalid as the percentage sign has not been properly encoded -->
<img alt="" src="" />

<!-- This is valid as the percentage sign has been encoded as %25 -->
<img alt="" src="" />

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Related W3C validator issues