+

The + character has three functions in CQL.

First, it is the symbol for addition:

  2+4 ≡ 6
  #♘ + #♞ ≡ #♘♞

Second, (since CQL 6.1) it is the symbol for string concatenation:

  "pin" + "mate" ≡ "pinmate"

Third, it is a symbol for a regular expression special character denoting repetition 1 or more times inside a line filter:

  ⊢ -- check+

Of course, + denotes "check" inside a PGN file, but this meaning is not used within CQL files themselves.