In the paper On the O'Nan Scott Theorem for primitive permutation groups the notation $A{.}B$ appears, meaning that $A$ is a group extension of $B$. On the same page, a similar notation appears:
$W = \{ (a_1, \ldots, a_k).\pi \mid a_i \in \operatorname{Aut}(T), \pi \in S_k, a_i \equiv a_j \mod{\operatorname{Inn}(T)} \mbox{ for all } i,j \}$
But what does the notation $g{.}h$ applied to elements of some group mean?