2.2.1 [XML] Section 2.1, White Space Handling

C0005:

The specification states:

 The value "default" signals that applications' default white-space processing 
 modes are acceptable for this element; the value "preserve" indicates the 
 intent that applications preserve all the white space. This declared intent is 
 considered to apply to all elements within the content of the element where it 
 is specified, unless overridden with another instance of the xml:space attribute. 
 This specification does not give meaning to any value of xml:space other than 
 "default" and "preserve". It is an error for other values to be specified; the 
 XML processor MAY report the error or MAY recover by ignoring the attribute 
 specification or by reporting the (erroneous) value to the application. 
 Applications may ignore or reject erroneous values.

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An error is reported if the xml:space attribute is used with a value other than default or preserve.