The + character has two functions in CQL.

First, it is the symbol for addition:

  2+4  6
  #N + #n  #[Nn]

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

  line --> check+

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