Some languages (e.g. Czech, Croat, Dutch, Hungarian, Latvian, Lithuanian, Maltese, Slovak, or Spanish) use two characters to represent a single phoneme; those double characters (dz, ij, ch) are called digraphs.
Digraphs are treated as single ‘letters’ on their own right. They influence hyphenation, abbreviation, and alphabetic order. Digraphs function as letters for the purposes of sorting e.g. in Czech, Slovak, Spanish and Welsh ‘ch’ serves as a single unit and words beginning with ‘ch’ have their own section in a dictionary.
Digraphs should not be confused with ligatures which are graphically stylized combinations of two or more letters. Whilst some ligatures indicate that successive sounds are to be pronounced as one (a,o) most of them are just typographical letter-combination, trying to improve a appearance of the words and eliminate possibly conflicting characters pairs (ff, fi, fl, ffi, fl). Those ligatures have a practical significance only for typesetting, and do not represents a semantic difference.
Proportional fonts (e.g. Fedra Sans) use regular string of letters to represent digraphs, and don’t require designing special characters. However, since all the characters in monospaced fonts must have the same widths, a special collection of digraphs has to be drawn for monospaced fonts (e.g. Fedra Mono). Unlike ligatures, digraphs should be case-consistent, with both upper, and lower case variants of the digraphs. It is important to understand that althought some digraphs in Fedra Mono may be graphically stylized, they are not ligatures, and are not meant to be used in languages which do not require use fixed-width digraphs.◀ Back
Combination of two letters that represent one phoneme needs to be represented by a single glyph in monospaced fonts.