Restrict Param Value setting to a Operator Defined Set

[kensipe]

It would be great if we could restrict params being set at install / update / upgrade to a set of predefined values... lets say a param defines a protocol or an output to json or xml and those are the only 2 valid options... the install should fail if out of range.

restrictions might include: set of string values ("xml", "json") numbers with min, max numbers odd, even (for example for quorum)

Issues:

• what to do if the restriction is narrowed for an upgrade?