Should I modify the form variable or the query variable? (31359)

Question1: Should I modify the form variable or the query variable?

Question2: What does the transformation expression mean?

Question1: Should I modify the form variable or the query variable?

Answer1: Whether you have to modify the form variable or the query variable depends on the where the value occurs.

Form variables are in the text following the URL.

Query variables are in the URL itself after the '?' symbol.

Question2: What does the transformation expression mean?

Answer2: The transformation is saying, if the text matches anything in group1, then replace the string with group1 (ie leave the string as is). If it fails to match anything in group1, then discard the string. Reg expression groups are identified by ().

For example, in the following rule:

Transform: (?i)(string1|string2|string3)|(.*)

into: (?1$1)

Group1 and group2 are the following:

group1 = string1|string2|string3

group2 = .* (which matches everything)