From Bright Pattern Documentation
The Set Variable block sets a value for a workflow variable.
This is the name of the variable. The Variable name can be set to be anything you like.
Value is the desired variable value. Variables in the $(varname) format can be used as values. Values can be specified as either expressions or literal strings. Literal strings are passed exactly as entered.
Expressions must begin with assignment sign = as the first character. For example, 2+2 will produce 2+2, whereas =2+2 will produce 4. The expression result produces one of the following data types: strings, integers, and floating point numbers.