Expression terms are always defined as values of XML attributes. Expression
terms use characters that have special meanings in the XML:
Single quotes for string constants.
In the XML, attribute values can be delimited by double quotes (") or
single quotes ('). If an expression contains string constants, it must
be delimited by double quotes in the metrics definition file
(e.g. condition="visibility='public'", not
condition='visibility='public''). Otherwise, XML parsers
will report an error.
operators &, <, and >.
The and operator & is an escape character in the XML. Likewise,
the operators < and > are used in the XML to delimit XML tags.
Some XML parsers will report an error if these
characters are used in XML attributes. To remedy this, you have
Denote the characters by their escape sequence, if your XML editor
does not automatically translate the characters for you:
& - &
< - <
> - >
Use the alternative notations: and instead of & lt and le instead of < and <= gt and ge instead of > and >= in instead of ->