generate a warning/error if tag is not specified

[Gianmaria Lari]

Suppose that I define a variable so that according to a tag I can generate

a a a

or

a b a

Is there any way to make lilypond complaint with a compilation error/warning in case I don't  specify a \keepWithTag or \removeWithTag?

For example:

\version "2.19.81"

var = {

  a 

  \tag#'vera a 

  \tag#'verb b

  a

}

{\var}  #this should generate a warning   

{\keepWithTag #'vera \var} #this is ok!

{\keepWithTag #'verb \var} #this is ok!

{\removeWithTag #'vera \var} #this is ok!

%etc.

Thank you, g.