code: func NewLexer(rd io.Reader) *Lexer {
  	p := Lexer{}
  	p.rd = rd
  	p.lastByte = bufSize
  	p.buf = make([]byte, bufSize)
  	p.r = -1
  	p.fill()
  	return &p
  }
docs: // NewLexer returns a new Lexer whose buffer has the default size.