Operator Type:
Operator Scope of Action:
Operator Purpose:
Operator First Added:
Operator Last Altered:
Property [other Property type actions]
Query [operators of similar scope]
Data manipulation [other Data manipulation operators]
Baseline
As at baseline
Syntax note: Operators without any defined mandatory arguments may omit their empty closing parentheses
$N
The value of the numbered back-reference for the current query (agent or if() conditional).
The valid range for for N is from 0 (zero) to 9.
The back-reference $0 always refers to the the whole matched string (or sub-string) for the stated query regex, i.e. it may match all or part of the target string. $1 to $9 refer to any further defined back-references within the overall regex, i.e. sub-strings within $0.
Back-references are numbered in the order created. The order is usually left-to right in order the parentheses open, noting that this allows for nesting of back-references.
Query back-references are discussed in fuller detail here.