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HTML Guide

Document uses the Unicode Private Use Area(s), which should not be used in publicly exchanged documents.

This is a warning that a special character in the Unicode Private Use Area is being used at the document, which might cause it to not work the way you might expect in different browsers/environments.

If you’ve checked the document in different browsers and it’s working fine, you can safely ignore this warning.

What are private-use characters in Unicode?

Private-use characters are code points whose interpretation is not specified by a character encoding standard and whose use and interpretation may be determined by private agreement among cooperating users. Private-use characters are sometimes also referred to as user-defined characters (UDC) or vendor-defined characters (VDC).

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