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+%D \module
+%D   [       file=attr-lay,
+%D        version=2007.06.06,
+%D          title=\CONTEXT\ Attribute Macros,
+%D       subtitle=Viewerlayers,
+%D         author=Hans Hagen,
+%D           date=\currentdate,
+%D      copyright={PRAGMA ADE \& \CONTEXT\ Development Team}]
+%C
+%C This module is part of the \CONTEXT\ macro||package and is
+%C therefore copyrighted by \PRAGMA. See mreadme.pdf for
+%C details.
+
+\writestatus{loading}{ConTeXt Attribute Macros / Viewerlayers}
+
+%D Currently there is a limitation in mixed inline usage. This has to do with the fact
+%D that we have a stacked model but cannot determine where to revert to (as we can
+%D have AABBCCAA ranges). Maybe I'll solve that one day. It only affects nested inline
+%D layers and these make not much sense anyway. We'd have to store the complete nesting
+%D stack in the attribute in order to be able to cross pages and that demands a new
+%D mechanism.
+
+\unprotect
+
+\registerctxluafile{attr-lay}{1.001}
+
+% needs to work over stopitemize grouping etc
+
+\installcorenamespace{viewerlayer}
+
+\installcommandhandler \??viewerlayer {viewerlayer} \??viewerlayer
+
+\setupviewerlayer
+  [\c!state=\v!start,
+   \c!title=,
+   \c!export=\v!yes, % exportable is ugly
+   \c!printable=\v!yes,
+   \c!scope=\v!local, % maybe global but needs checking with layout
+   \c!method=\v!none]
+
+\appendtoks
+  \clf_defineviewerlayer
+       tag       {\currentviewerlayer}%
+       title     {\viewerlayerparameter\c!title}%
+       visible   {\viewerlayerparameter\c!state}%
+       editable  {\v!yes}%
+       export    {\viewerlayerparameter\c!export}%
+       printable {\viewerlayerparameter\c!printable}%
+       scope     {\viewerlayerparameter\c!scope}%
+  \relax
+  \doif{\viewerlayerparameter\c!method}\v!command
+    {\setuxvalue{\e!start#1}{\startviewerlayer[\currentviewerlayer]}%
+     \setuxvalue{\e!stop #1}{\stopviewerlayer}}%
+\to \everydefineviewerlayer
+
+\unexpanded\def\startviewerlayer[#1]{\clf_startviewerlayer{#1}}% not grouped
+\unexpanded\def\stopviewerlayer     {\clf_stopviewerlayer}     % not grouped
+\unexpanded\def\viewerlayer     [#1]{\groupedcommand
+                                    {\clf_startviewerlayer{#1}}% grouped
+                                    {\clf_stopviewerlayer}}    % grouped
+
+% some day we will keep this at the lua end as the info is only needed there
+
+\newtoks\currentviewerlayertoks % soon we can set macros at the lua end
+
+\def\currentviewerlayer{\the\currentviewerlayertoks}
+
+\appendtoks
+    \let\currentviewerlayer\empty
+\to \everybeforepagebody
+
+% layout components are implemented rather directly (speed)
+
+\installcorenamespace{layoutcomponentattribute}
+
+\def\attr_layoutcomponent_initialize#1%
+  {\edef\layoutcomponentboxattribute{\clf_definedlayoutcomponent{#1}}%
+   \edef\layoutcomponentboxattribute{attr \viewerlayerattribute \layoutcomponentboxattribute\relax}%
+   \expandafter\glet\csname\??layoutcomponentattribute#1\endcsname\layoutcomponentboxattribute}
+
+\def\attr_layoutcomponent_set#1% make this faster
+  {\expandafter\let\expandafter\layoutcomponentboxattribute\csname\??layoutcomponentattribute#1\endcsname
+   \ifx\layoutcomponentboxattribute\relax
+     \attr_layoutcomponent_initialize{#1}% get rid of { }
+   \fi}
+
+\def\attr_layoutcomponent_reset
+  {\let\layoutcomponentboxattribute\empty}
+
+\let\setlayoutcomponentattribute  \gobbleoneargument
+\let\resetlayoutcomponentattribute\relax
+\let\layoutcomponentboxattribute  \empty
+
+\unexpanded\def\showlayoutcomponents
+  {\let\setlayoutcomponentattribute  \attr_layoutcomponent_set
+   \let\resetlayoutcomponentattribute\attr_layoutcomponent_reset}
+
+\unexpanded\def\attr_layoutcomponent_cleanup
+  {\clf_cleanuplayers}
+
+\appendtoks
+    \attr_layoutcomponent_cleanup
+\to \everyshipout
+
+\protect \endinput