Question

Simple question. If I attempt to look at

<?xml version='1.0'?>
<test key="blah('foo=1&bar=2')">
</test>

in Firefox, it complains

XML Parsing Error: not well-formed
Location: file:///C:/tmp/dump2.xml
Line Number 2, Column 27:

<test key="blah('foo=1&bar=2')">
--------------------------^

Why is this? What do I need to escape?

Answer 1

<?xml version='1.0'?>
<test key="blah('foo=1&bar=2')">
</test>

is not well-formed XML. Use:

<?xml version='1.0'?>
<test key="blah('foo=1&amp;bar=2')">
</test>

EDIT:

Error message in Oxygen XML Editor:

F [Xerces] The reference to entity
“bar” must end with the ‘;’ delimiter.

That means &bar is parsed as entity reference, but here is syntax error, that is, missing ;. You need to escape & character using predefined entity (one of five) &.