How to use the French expression "s’il en est"?

Question

Certains permettent de faire d'une victime une marionnette obéissante. Une pratique interdite, s’il en est.

While I roughly understand the meaning of this expression, I find the definition in dictionaries somewhat lacking.

Given that there is no accord between the feminine noun "pratique" and "il", I assume this "il" is actually an impersonal, placeholder subject and the entire expression is synonymous with "s'il en existe une", for instance.

I wonder if this expression means something along the lines of:

If there were such a thing as a forbidden practice, this would be one.

A couple of example sentences with "s’il en est" would not go amiss!

Answer 1

Well it means exactly what you said but even more extreme :

If there were such a thing as ..., this would be THE one.

In French it is the same as “s'il en existe c'est bien celui-ci ou ceux-là”.

Source : Wiktionnaire.

Answer 2

I think it's more a figure of speech than anything else, it doesn't convey any meaning in particular, it's more to emphasis on the peculiarity of what is being talked.

But a more accurate understanding would be, among the forbidden practices that exist, this one is one of them and one of the top one (since the speaker put the effort to add this expression at the end of the sentence).

But it's not a common expression. I can't find any casual or professional use of this expression.

Answer 3

can be transkated into "If ever". C'est une expression un peu désuète en français.