code: function checkInterpolatedVariable(i) {
    const start = i;
    let l;
  
    if (i >= tokensLength) return 0;
  
    if (tokens[i].type !== TokenType.CommercialAt ||
        !tokens[i + 1] || tokens[i + 1].type !== TokenType.LeftCurlyBracket) {
      return 0;
    }
  
    i += 2;
  
    if (l = checkIdent(i)) i += l;
    else return 0;
  
    return tokens[i].type === TokenType.RightCurlyBracket ? i - start + 1 : 0;
  }
docs: Check if token is part of LESS interpolated variable
  @param {Number} i Token's index number
  @returns {Number}