Rigid vs flexible Bridge pattern

In a software design course, we've been given a term that I'm inclined to call "mysterious" since no internet search can reveal it. The term was given in a language native to my place, but the English translation for it would as follows: "rigid" or "hard" Bridge pattern vs the "soft" or "flexible" Bridge pattern. Gamma obviously fails to describe this.

What could this mean? I think experienced architects should be familiar with the two main different types of bridges, even if they call that differently.
Is there a book on patterns more realistic and containing more experience that the Gamma et al. reference book?

The last question can be deemed opinion based according to the rules, feel free to remove it, but leave the Bridge question intact. Thank you for understanding.

Solution

Alright, so here is the answer, as per the coach:

"soft" or "flexible" is when there is no implementation pointer field in the abstraction class, and the said pointer is passed as a parameter to the wrapper method of the abstraction class every time an implementation method is called via the above mentioned wrapper
"hard" or "rigid" bridge is when there is such a pointer field in the abstraction class, it is declared private, and the implementation methods are wrapped with protected methods inside the abstraction class

I wholeheartedly hate making UML or any other kind of diagram using a PC (as opposed to paper and pencil) so this time words have to suffice :) If posting a hand-made picture is fine, I'll add one.

There is no literature covering these details indeed, this has turned out to be a bit of proprietary knowledge, mirrored only by a number of scholarly articles.