function getIndentText(firstToken) {
    const text = sourceCode.text
    let i = firstToken.range[0] - 1

    while (i >= 0 && !LT_CHAR.test(text[i])) {
      i -= 1
    }

    return text.slice(i + 1, firstToken.range[0])
  }
Get the text of the indentation part of the line which the given token is on.
@param {Token} firstToken The first token on a line.
@returns {string} The text of indentation part.