PAL

Ptolemaeus Arabus et Latinus

_ (the underscore) is the placeholder for exactly one character.
% (the percent sign) is the placeholder for no, one or more than one character.
%% (two percent signs) is the placeholder for no, one or more than one character, but not for blank space (so that a search ends at word boundaries).

At the beginning and at the end, these placeholders are superfluous.

circonférence ‘circumference’

French

References: PH Morelon: I.3:1, 18:7; I.18, 70
Translation of:
Arabic: الخطّ المحيط [PH Morelon: I.3:1, 19:5]
Arabic: دور [PH Morelon: I.18, 71:15]