code: function getDimension() {
    const type = NodeType.DimensionType;
    const token = tokens[pos];
    const line = token.ln;
    const column = token.col;
    const content = [
      getNumber(),
      getUnit()
    ];
  
    return newNode(type, content, line, column);
  }
docs: Get node of a number with dimension unit
  @return {Node}