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An [XML] document is [WellFormed] if it parses correctly. The main issue that causes [XML] not to be [WellFormed] is tag ordering. For example the following is [WellFormed]:

 ...
 <a>
 this is well formed </b>
 <c> this is well formed too </c>
 </a>
 ...

while this is not:

 ...
 <a>
 this is well formed <b>
 <c> this is well formed too
 </a>
 ...

In the second fragment, neither the <b> nor the <c> tag are closed. Unlike [SGML], [XML] does not allow tags to be automatically closed when the enclosing tag is closed. This is the reason why the <p> tag in [HTML]/[XHTML] gives people grief---in [HTML] you only need to put in the opened tags while in [XHTML] you need to put in both the opening and the closing tag.

The tag pattern:

 <a> ... <b> ... </a> ... </b>

is not WellFormed in either [SGML] or [XML], if you want non-nesting overlapping ranges such as this you need something like:

 <a id="1"/> ... <b id="2"/> ... <a id="1"/> ... <b id="2"/>

then you can reconstruct either of the tags as necessary.

[WellFormed] [XML] differs from [Valid] [XML] in that [Valid] [XML] has been (or could be) checked against a [Schema] or [DTD].

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Version 1, saved on Thursday, August 21, 2003 12:09:47 pm by StuartYeates

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