src/vs/editor/common/model/bracketPairsTextModelPart/bracketPairsTree/bracketPairsTree.ts/BracketPairsTree/getFirstBracketBefore
class BracketPairsTree:	public getFirstBracketBefore(position: Position): IFoundBracket | null {
		const node = this.initialAstWithoutTokens || this.astWithTokens!;
		return getFirstBracketBefore(node, lengthZero, node.length, positionToLength(position));
	}