An XML document is said to be well formed if it follows it’s syntax rules very closely. The rules that must apply to an XML document are listed below:
All XML elements must have closing tags
Example
<book>
<title>Harry Potter series</title>
<author>J.K.Rowling</author>
</book>
XML tags are case-sensitive
Opening and closing tags must be written in same case.
Example
<title>Harry Potter series</title> <!--- Correct --->
<title>Harry Potter series</Title> <!--- Not correct --->
XML tags must be properly nested
Unlike HTML, XML is sensitive to the order of tags.
Example
<b><i>See the order of tags</b></i> //Valid in HTML but invalid in XML.
XML documents must have the root element
The root element s the parent to all other elements in the document.
Example
<root>
<child>
<sub-child>…</sub-child>
</child>
</root>
XML attributes are set in name:value pair
The name:value pair gives more information on the tag itself. The value should be quoted as shown below.
Example
<book type=”fiction”>
<title>Harry Potter series</title>
<author>J.K.Rowling</author>
</book>
Parsing properly the predefined entities
If a XML document has predefined entity such as “<”, “>” etc... which will be interpreted by parser as start or end of new element, it has to be replaced with entity references. The entity references and it’s symbol are listed below:
< - <
> - >
& - &
‘ - '
“ - "
Example
<p>Sanju & Geetha are friends </p> <!--- Not correct --->
<p>Sanju & Geetha are friends </p> <!--- Not correct --->
Properly adding comments
To add a comment <!---- comment here ---->
symbol is used as in HTML.
Preservation of white spaces
White spaces are preserved in XML and not truncated as in HTML.
Example
<p>May June</p> is not same as
<p>May June</p>
New line storage
A new line is stored as LF.
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