code: function checkArgument(i) {
    let l;
  
    if (l = checkEscapedString(i)) tokens[i].argument_child = 1;
    else if (l = checkDeclaration(i)) tokens[i].argument_child = 2;
    else if (l = checkVariablesList(i)) tokens[i].argument_child = 3;
    else if (l = checkVariable(i)) tokens[i].argument_child = 4;
    else if (l = checkSC(i)) tokens[i].argument_child = 5;
    else if (l = checkUnary(i)) tokens[i].argument_child = 6;
    else if (l = checkOperator(i)) tokens[i].argument_child = 7;
    else if (l = checkDelim(i)) tokens[i].argument_child = 8;
    else if (l = checkDeclDelim(i)) tokens[i].argument_child = 9;
    else if (l = checkString(i)) tokens[i].argument_child = 10;
    else if (l = checkPercentage(i)) tokens[i].argument_child = 11;
    else if (l = checkDimension(i)) tokens[i].argument_child = 12;
    else if (l = checkNumber(i)) tokens[i].argument_child = 13;
    else if (l = checkUri(i)) tokens[i].argument_child = 14;
    else if (l = checkFunction(i)) tokens[i].argument_child = 15;
    else if (l = checkIdent(i)) tokens[i].argument_child = 16;
    else if (l = checkVhash(i)) tokens[i].argument_child = 17;
    else if (l = checkBlock(i)) tokens[i].argument_child = 18;
    else if (l = checkParentheses(i)) tokens[i].argument_child = 19;
  
    return l;
  }
docs: Check if token is valid to be part of arguments list.
  @param {Number} i Token's index number
  @returns {Number}