This is an addon that demonstrates various techniques available in World of Warcaft's UI XML.
Based on a conversation in #wowuidev IRC, I wanted to see how an addon might be able to use the <ScopedModifier> XML tag. The tag on it's own seems to do nothing. The same is true of two known attributes: forbidden and fullLockdown. These are likely related to internal secure code, and are only usable by Blizzard addons.
The third attriute, scriptsUseGivenEnv, could actually be quite useful to community addons. This attribute allows an XML to use a mixin that is keyed into the private addon table. See the code for an example.
This may need further testing, but it seems that it only effects the mixin widget attribute and the associated method attribute for scripts. Any string used in a text attribute are not found, as well as function for widget scripts.