#using

( specific directive - since version 2.0.7 )

Checks if all the given objects are defined in the Velocity context
Throws an error if one of the given objects is not defined
Useful to check the specific variables existence

Examples :

    #using( "var1" )
    #using( "var1", "var2" )
    #using( "var1", "var2", "foo", "bar" )

    #using( '$var1' )
    #using( '$var1', '$var2' )