params and paramDefaults support looking up the parameter value from the
data object. The syntax for that is `@nested.property.name`.
Currently, $resource uses $parse to do this. This is too liberal
(you can use values like `@a=b` or `@a | filter` and have it work -
which doesn't really make sense). It also puts up a dependency on
$parse which is has restrictions to secure expressions used in
templates. The value here, though a string, is specified in Javascript
code and shouldn't have those restrictions.
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