  We give structural results about bifibrations of (internal)
$(\infty,1)$-categories with internal sums. This includes a higher version of
Moens' Theorem, characterizing cartesian bifibrations with extensive aka stable
and disjoint internal sums over lex bases as Artin gluings of lex functors.
  We also treat a generalized version of Moens' Theorem due to Streicher which
does not require the Beck--Chevalley condition.
  Furthermore, we show that also in this setting the Moens fibrations can be
characterized via a condition due to Zawadowski.
  Our account overall follows Streicher's presentation of fibered category
theory \`{a} la B\'{e}nabou, generalizing the results to the internal,
higher-categorical case, formulated in a synthetic setting.
  Namely, we work inside simplicial homotopy type theory, which has been
introduced by Riehl and Shulman as a logical system to reason about internal
$(\infty,1)$-categories, interpreted as Rezk objects in any given
Grothendieck--Rezk--Lurie $(\infty,1)$-topos.
