The ISO Latin 1 character repertoire – a description with usage notes, section 4 Explanations and notations:

The notation U+nnnn

Unicode characters are commonly referred to using a notation like
where nnnn is a four-digit hexadecimal (base 16) number specifying the code position of the character in Unicode. For example, the space character has the same code number in Unicode as in ISO 8859-1, namely 32 decimal, 20 hexadecimal; thus, it can be denoted as U+0020. Generally, a notation like U+nnnn is needed for referring to characters uniquely in contexts where one cannot reliably present the character itself.

Originally created 2000-03-31. Structurally changed 2018-10-16. Minor modifications 2018-12-15.
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