2.2.56 [HTML] Section 24.3, Character entity references for symbols, mathematical symbols, and Greek letters
The specification states:
To support these entities, user agents may support full [ISO-10646] or use other means. Display of glyphs for these characters may be obtained by being able to display the relevant [ISO-10646] characters or by other means, such as internally mapping the listed entities, numeric character references, and characters to the appropriate position in some font that contains the requisite glyphs.
All Document Modes (All Versions)
Character entities for symbols, mathematical symbols, and Greek letters is supported by displaying the relevant glyphs from [ISO-10646].