HTML Checking for Large Sites

The only permitted value for the xmlns attribute is http://www.w3.org/2000/svg.

The namespace declaration for an <svg> element is provided by the xmlns attribute like this:

<svg xmlns="http://www.w3.org/2000/svg">
  <!-- more tags here -->
</svg>

Although using https in the URL looks like it’s going to be more secure, in fact this URL is not used to connect it to, only to declare the namespace.

A <pattern> element has been found with an invalid ID. Check the format of the ID and ensure it does not start with a digit, full stop (.) or hyphen (-).

The <pattern> element is used within <svg> elements, which use XML 1.0 syntax. That syntax specifies that valid IDs only include designated characters (letters, digits, and a few punctuation marks), and do not start with a digit, a full stop (.) character, or a hyphen-minus (-) character.

A tag starting with <? has been found within the document, but it’s not supported. Probable causes can be:

• Copy-pasting the contents of an SVG file. If you do that, you should only paste the <svg>...</svg> part, but not the first line with <?xml...>.
• Unprocessed <?...> tags on server scripting languages like PHP, like <?php>

Learn more:

• [freeCodeCamp: How to Use SVG Images in CSS and HTML]https://www.freecodecamp.org/news/use-svg-images-in-css-html/)