Every glyph of every writing system follows a specific structure for its parts (positioning of the strokes in relation to each other). People reading words and texts in a given script would recognize the glyphs (letters, characters, symbols, etc.) if their structure follows a convention that is familiar to all of users.

Due to the evolution of each script, the structure can change over time (e.g., Fraktur styles), or have multiple variants (e.g., single and double storey a).