REG_MULTI_SZ
An expression that evaluates to TRUE or FALSE. When the expression evaluates to FALSE, the application is present but disabled on the Tools menu. SMS writes an error value to the application key as an aid to ISV debugging. If no expression is specified here, EnableRule defaults to TRUE. The syntax and use of the expression are the same as for PresentRule.
This value is examined only under a specified context key when the current context matches that context key.
EnableRule is REG_MULTI_SZ for readability when using regedt32 to view Registry settings. SMS treats nulls as white space when parsing this value.