In computing, a Unicode symbol is a Unicode character which is not part of a script used to write a natural language, but is nonetheless available for use as part of a text.
Many of the symbols are drawn from existing character sets or ISO/IEC or other national and international standards. The Unicode Standard states that "The universe of symbols is rich and open-ended," but that in order to be considered, a symbol must have a "demonstrated need or strong desire to exchange in plain text." This makes the issue of what symbols to encode and how symbols should be encoded more complicated than the issues surrounding writing systems. Unicode focuses on symbols that make sense in a one-dimensional plain-text context. For example, the typical two-dimensional arrangement of electronic diagram symbols justifies their exclusion. (Legacy characters such as box-drawing characters, Symbols for Legacy Computing and the Symbols for Legacy Computing Supplement, are an exception, since these symbols largely exist for backward compatibility with past encoding systems; a number of electronic diagram symbols are indeed encoded in Unicode's Miscellaneous Technical block.) For adequate treatment in plain text, symbols must also be displayable in a monochromatic setting. Even with these limitations – monochromatic, one-dimensional and standards-based – the domain of potential Unicode symbols is extensive. (However, emojis – ideograms, graphic symbols – that were admitted into Unicode, allow colors although the colors are not standardized. Color-dependent emojis are traditionally rendered using hatching in monochromatic settings.)
