\input regression-test.tex
\documentclass{article}
\usepackage[mode=script]{osglecture-modes}

\DeclareModeBehaviorClass{dynamic}
\DeclareModeBehaviorClass{longform}
\AssignLectureModeBehavior{slides,handout}{dynamic}
\AssignLectureModeBehavior{script,article}{longform}

\ExplSyntaxOn
\cs_new_protected:Npn \osg_test_dynamic:n #1
  { \TYPE{DYNAMIC~#1} }
\cs_new_protected:Npn \osg_test_longform:n #1
  { \TYPE{LONGFORM~#1} }
\ExplSyntaxOff

\DeclareModeAwareCommand{\SemanticCommand}{dynamic,longform}
\ExplSyntaxOn
\DeclareModeAwareCommandImplementation
  {\SemanticCommand}{dynamic}{\osg_test_dynamic:n}
\DeclareModeAwareCommandImplementation
  {\SemanticCommand}{longform}{\osg_test_longform:n}
\cs_new_protected:Npn \osg_test_incomplete:n #1
  { \TYPE{INCOMPLETE~ACTIVE~#1} }
\ExplSyntaxOff

\DeclareModeAwareCommand{\IncompleteCommand}{dynamic,longform}
\ExplSyntaxOn
\DeclareModeAwareCommandImplementation
  {\IncompleteCommand}{longform}{\osg_test_incomplete:n}
\msg_redirect_name:nnn
  {osglecture_modes}{missing-implementation}{none}
\ExplSyntaxOff

\newcommand\SimpleCommand{\TYPE{SIMPLE}}
\MakeOverlayAwareCommand[default-mode=presentation]{\SimpleCommand}

\newcommand\FlattenedCommand{\TYPE{FLATTENED}}
\MakeOverlayAwareCommand[fallback=flatten]{\FlattenedCommand}

\newcommand\OmittedCommand{\TYPE{OMITTED}}
\MakeOverlayAwareCommand[fallback=omit]{\OmittedCommand}

\NewDocumentCommand\OptionalCommand{o}
  {
    \IfNoValueTF{#1}
      {\TYPE{OPTIONAL NONE}}
      {\TYPE{OPTIONAL #1}}
  }
\MakeOverlayAwareCommand
  [arguments={o},default-mode=presentation,fallback=flatten]
  {\OptionalCommand}

\begin{document}
\START
\SemanticCommand{CONTENT}
\IncompleteCommand{BRANCH}
\SimpleCommand
\SimpleCommand<script>
\FlattenedCommand<2->
\OmittedCommand<2->
\OptionalCommand<presentation>[HIDDEN]
\OptionalCommand<script>[VISIBLE]
\OptionalCommand<2->[FLATTENED-ARGUMENT]
\begingroup
  \MakeOverlayAwareCommand
    [arguments={s o},default-mode=script]
    {\\}
  First\\<script>[1ex]Second
  \\<presentation>[4ex]Third
\endgroup
\TYPE{LINEBREAK ARGUMENTS CONSUMED}
\END
\end{document}