Parser for operator precedence reshuffling and parentheses

Grammar Cells in MPS use a parser to deconstruct an expression tree into tokens and to rebuild a new tree that has the same textual representation, but respects the operator precedence rules.

In case of parentheses the editor supports inserting text without immediately creating a node for it (it's an annotation, so while it actually is a node it's one that has no semantic meaning yet). It tries to parse the tokens into a valid expression tree until the users inserts a matching pair of parentheses.

Start by locating the Grammar Cells parser responsible for deconstructing expression trees into tokens and rebuilding them with operator precedence. Study how parentheses are represented as non-semantic annotations and how parsing handles an unmatched versus matching pair; done means expressions preserve their textual representation while producing a precedence-correct tree.