Variable mappingValuePatternConst

mappingValuePattern: "^=(?:([^:.]+|'[^']+')?(?::([^.:]+)?)?\\.)?([A-Z]+[1-9][0-9]*)|('[^']+'|[^=].*)$" = ...

This regular expression matches a value reference, i.e. the value of a node in the mapping object. They are always strings!

The captures are:

0: the entire reference 1: a possibly single-quoted sheet name or undefined 2: a section name without the leading colon or undefined 3: a cell name without the leading dot or undefined 4: a literal value, possibly with a leading single-quote, or undefined