Following rules apply to an XML document with valid element and attribute properties.

XML Elements

In XML document the elements are said to be well formed if:

  • Opening tag is subsequently closed.
  • If there is any empty element, it has to be terminated.
  • The nested tags should not overlap and should be properly nested.
  • A single element called root element contains all other elements.
  • All elements are well formed.

Example of well-formed XML elements






Example of non-well-formed XML elements


      <country><b>Russia</country></b> -> Elements not nested properly



      <br> -> Empty element, not closed.

</Earth> -> Ending element has different name.

XML Attributes

The attributes add extra information to the elements. The well formed XML attributes have following characteristics:

  • It has to be single or double quoted.
  • Attributes cannot have multiple values and can appear at most once on each element.
  • If more than one value is desired (example, CSS class names or identifier names) it should be well-formed with some format which does not cause parsing error in XML and the quotes does not cause problem.
  • Attributes cannot have tree structure.
  • The attribute values are separated by comma or semi-colon or space–delimited list.

Example of well-formed XML attributes

The example shows multiple attribute names and attribute name “class” has multiple values “style1” and “style2”. This is well-formed attribute.

<earth totalArea="100">



<div class=”style1 style2”>


Example of non well-formed XML attributes

<earth totalArea="100" population=”100”>



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