code: func ParseMetricSelector(input string) (m []*labels.Matcher, err error) {
  	p := newParser(input)
  	defer p.recover(&err)
  
  	name := ""
  	if t := p.peek().typ; t == ItemMetricIdentifier || t == ItemIdentifier {
  		name = p.next().val
  	}
  	vs := p.VectorSelector(name)
  	if p.peek().typ != ItemEOF {
  		p.errorf("could not parse remaining input %.15q...", p.lex.input[p.lex.lastPos:])
  	}
  	return vs.LabelMatchers, nil
  }
docs: // ParseMetricSelector parses the provided textual metric selector into a list of
  // label matchers.