If it's not documented in the below substitution tutorial then it doesn't exist.
www.joomlapolis.com/support/tutorials/107-use-cases/18353-using-substitutions-throughout-cb
To test against multiple values you use "or" usage as noted in the above tutorial or use a REGEXP operator. Example as follows.
[cb:if username="demo" or username="admin"]This is Demo or Admin being displayed.[/cb:if]
The bottom of the tutorial has several usage examples including the above example. REGEXP example as follows.
[cb:if username=~"/demo|admin/"]This is Demo or Admin being displayed.[/cb:if]