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.

always invisible ‘always invisible’

English

References: Alm. Toomer: 83; 84
Translation of:
Greek: ἀεὶ ἀφανής [Alm. Heiberg: II.6, 103:4; II.6, 104:8; II.6, 117:6]
Synonyms:
ever-invisible[Alm. Toomer: 90]