extensions/references-view/src/references/model.ts/ReferencesModel/_prefixLen
class ReferencesModel:	private static _prefixLen(a: string, b: string): number {
		let pos = 0;
		while (pos < a.length && pos < b.length && a.charCodeAt(pos) === b.charCodeAt(pos)) {
			pos += 1;
		}
		return pos;
	}