// Comment assignment state.
	pre  []Expr // all expressions, in preorder traversal
	post []Expr // all expressions, in postorder traversal
}

func newInput(filename string, data []byte) *input {
	return &input{
		filename:  filename,
		complete:  data,
		remaining: data,
		pos:       Position{Line: 1, LineRune: 1, Byte: 0},
	}
}