a0d929ca_WSRP_v2_0_Specification__Statement_text
[#] CS138 [Section] 9.2 [Statement text] 
Since the values a Portlet provides will appear as either an URL parameter value or as part of the path of an URL, these values it MUST be strictly encoded (i.e. "&", "=", "/", and "?" need to be url-escaped) so that special URL characters do not invalidate the processing of the enclosing URL.
WSRP v2.0 Specification
Statement text