Module ids 

Element ids kept across edits: a file’s new parse matched against its last, sibling list by sibling list, so an element keeps its id however the lines around it change. Siblings with a key are matched by it; the others by a shortest edit script over the list (Myers’ diff), comparing each element’s name and own attributes, and then, among what is left between two matches, an element with one of the same name, in order, as an edit of it. A matched element’s children are matched the same way; an element left over is new and takes the file’s next id.

The cost is a pass over the file: lists are trimmed of what they share at either end, and an edit script longer than MAX_EDITS gives way to matching the rest in order, so no list costs more than its length times that.

Constants

MAX_EDITS

The longest edit script searched for between two lists of siblings.

Functions

key

The key an element names itself by among its siblings, if it has one.

matched

new, its elements given the ids of the elements of last they match, and fresh ones from last’s next id where they match none.