a quality of writing (print or handwriting) that can be easily read
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Legibility \Leg`i*bil"i*ty\ (l[e^]j`[i^]*b[i^]l"[i^]*t[y^]), n. The quality of being legible; legibleness. --Sir. D. Brewster.
Both Sellars and Morris love various kinds of gestural sign-language, but Sellars' use of it is incompetent in terms of theatrical legibility or dynamics.
But it has been adapted to accelerate the transmission and improve the legibility of the printed message.