The `myvar` column, which holds the variable size, **MUST** be an `Int_t` (/I).
message should also explicitly appear immediately in the TTree → “fundamental types” section, at the end of the “Examples:” (it’s called there “myvar” instead of “nelem”), as almost nobody will ever read the TTree::Branch method description (well, even I forgot that it needed fixes, too).
And maybe modify also:
... and the size of which is stored in an `Int_t` (/I) branch called `myArrSize`, ...`
@couet Just see the last point in the TTree → “fundamental types” section … I propose to modify it a bit (instead of “in a branch”, explicitly say “in an Int_t (/I) branch”).