This method will return the length of types that can be bound
by a size constraint (BIT STRING, OCTET STRING, character string,
and SEQUENCE OF/SET OF).
Return the length of the MDER encoding for this type, assuming that
the type is NOT a fixed length OCTET STRING (if it is fixed length, you
need not call this method!).
This method will convert the given string value into XML character
content by escaping special characters in the sting such as
ampersand (&), left angle bracket (<), etc..