Homoglyph

In orthography and typography, a homoglyph is one of two or more graphemes, characters, or glyphs with shapes that appear identical or very similar. The designation is also applied to sequences of characters sharing these properties.

Synoglyphs are glyphs that look different but mean the same thing. Synoglyphs are also known informally as display variants.The term homograph is sometimes used synonymously with homoglyph, but in the usual linguistic sense, homographs are words that are spelled the same but have different meanings, a property of words, not characters.

In 2008, the Unicode Consortium published its Technical Report #36 on a range of issues deriving from the visual similarity of characters both in single scripts, and similarities between characters in different scripts.

A manifestation of homoglyphic confusion in a historical regard results from the use of a 'y' to represent a 'þ' when setting older English texts in typefaces that do not contain the latter character. It has led in modern times to such phenomena as Ye olde shoppe, implying incorrectly that the word the was formerly written ye /jiː/. For further discussion, see thorn.

Typefaces containing homoglyphs are considered unsuitable for writing formulas, URLs, source code, IDs and other text where characters cannot always be differentiated without context.

Two common and important sets of homoglyphs in use today are the digit zero and the capital letter O (i.e. 0 & O); and the digit one, the lowercase letter L and the uppercase i (i.e. 1, l & I). In the days of mechanical typewriters there was very little or no visual difference between these glyphs and typists treated them interchangeably as keyboarding shortcuts. In fact, most keyboards did not even have a key for the digit "1", requiring users to type the letter "l" instead, and some also omitted 0. As these same typists transitioned in the 1970s and 1980s to being computer keyboard operators, their old keyboarding habits continued with them in their new profession, and became a source of great confusion.

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