A semantic version selector (short: semsel) is a string that can match only onto specific semantic versions (semver). A semsel mainly consists of one or multiple comperators combined with inner logical ANDs and outer ORs.
A complete example could look like this:
>0.0.1-b.1337 <=0.0.2- || 0.0.3 +debug* || ~1.0 || 2.0.x +with* || 2.1.0- - 2.1.1- !2.1.1-b.9 || [3.1,3.3)