how explain difference of usage of mpdf-variables

[Klap-in]

How explain difference between:

• variables that are could be used as attributes ($mpdf->variablename)
• and these that could be only use as configuration parameter in the $config array of the mPDF constructor?

I spot that sometimes is written:
Set as a <a href="{{ "/configuration/configuration-v7-x.html" | prepend: site.baseurl }}">configuration variable</a>

And /reference/mpdf-variables/overview.html lists a lot of variables that only should be used on initiation of DOCUMENT.

But from the variable pages this difference in usage is not clear.
Who has suggestions for a simple manner to make these difference in usage clear on the variable pages?