Predefined entities in XML language

The special characters for quote ("), apostrophe ('), less-than (<), greater-than (>), and ampersand (&) are used for punctuation in XML, and are represented with predefined entities: ", ', <, >, and &. Notice that the semicolon is part of the entity.You cannot use "<" or "&" in attributes or elements, as the following series of examples demonstrates.

select xmlparse("<a atr='<'/>")

Msg 14702, Level 16, State 0:
Line 1:
XMLPARSE(): XML parser fatal error <<A '<' character cannot be used in attribute 'atr', except through <&gt;> at line 1, offset 14.

select xmlparse("<a atr1='&'>")

Msg 14702, Level 16, State 0:
Line 1:
XMLPARSE(): XML parser fatal error 
<<Expected entity name for reference>> 
at line 1, offset 11

select xmlparse("<a> < </a>")

Msg 14702, Level 16, State 0:
Line 2:
XMLPARSE(): XML parser fatal error
<<Expected an element name>>
at line 1, offset 6.

select xmlparse(" & ")
Msg 14702, Level 16, State 0:
Line 1:
XMLPARSE(): XML parser fatal error
<<Expected entity name for reference>>
at line 1, offset 6.

Instead, use the predefined entities < and &, as follows:

select xmlextract("/",
    "<a atr='&lt; &amp;'> &lt; &amp; </a>" )
--------------------------------
          <a atr="&lt; &amp;"> &lt; &amp; </a>

You can use quotation marks within attributes delimited by apostrophes, and vice versa. These marks are replaced by the predefined entities " or '. In the following examples, notice that the quotation marks or apostrophes surrounding the word 'yes' are doubled to comply with the SQL character literal convention:

select xmlextract("/", "<a atr=' ""yes"" '/> " ) 
---------------------------------
           <a atr=" "yes" "></a>

select xmlextract('/', '<a atr=" ''yes'' "/> ' )
----------------------------
            <a atr=" 'yes' "></a>

You can use quotation marks and apostrophes within elements. They are replaced by the predefined entities " and &apol:, as the following example shows:

select xmlextract("/", " ""yes"" and 'no' " )
-------------------------------------
          &quot;yes&quot; and 'no'

You can also use “>” in attributes or elements, and it is replaced by the predefined entity >, as this example demonstrates:

select xmlextract("/", "<a atr='>'>  >  </a>" ) 
----------------------------------------------
          <a atr="&gt;"> &gt; </a>