Variable

Variables

The assigned variable is always the name of the new variable.

Evaluate

Uses (multiple) other variables and evaluates their values to assign the new variable).

Regular expression

Uses a match group to extract a text from an input, e.g.: prefix(.*?)suffix

the non-greedy regular expression returns the inner text between prefix and suffix.

Spring EL

Spring expression language for advanced cases, see Spring Documentation or some tutorials like this.