code: function checkUri(i) {
    const start = i;
    let l;
  
    if (i >= tokensLength || tokens[i].value !== 'url') return 0;
  
    // Skip `url`.
    i++;
  
    if (i >= tokensLength || tokens[i].type !== TokenType.LeftParenthesis)
      return 0;
  
    // Store the opening parenthesis token as we will reference it's `right`
    // property to determine when the parentheses close
    const leftParenthesis = tokens[i];
  
    // Skip `(`.
    i++;
  
    // Determine the type of URI
    while (i < leftParenthesis.right) {
      if (l = checkUri1(i)) {
        i += l;
        tokens[start].uriType = 1; // Raw based URI (without quotes)
      } else if (l = checkUri2(i)) {
        i += l;
        tokens[start].uriType = 2; // Non-raw based URI (with quotes)
      } else return 0;
    }
  
    // Skip `)`.
    i++;
  
    return i - start;
  }
docs: Check if token is part of URI, e.g. `url('/css/styles.css')`
  @param {number} i Token's index number
  @returns {number} Length of URI