Returns the URL (as a string) associated with this help resource.
Returns:
the URL (as a string) associated with the resource
Valid URL of a help resource is:
a /pluginID/path/to/resource, where
pluginID is the unique identifier of the plugin
containing the help resource,
path/to/document is the help resource path,
relative to the plugin directory.
For example. /myplugin/mytoc.xml or
/myplugin/references/myclass.html are vaild.
string representation of URI to an external document. In
this case, all special characters have to be enoded such that the
URI is appropriate to be opened with a web browser.
http://eclipse.org/documents/my%20file.html and
jar:file:/c:/my%20sources/src.zip!/mypackage/MyClass.html
are examples of valid URIs.