Support for <indexterm>s when reading DocBook (#7607)

* Support for <indexterm>s when reading DocBook
* Update implementation status of `<n-ary>` tags
* Remove non-idiomatic parentheses
* More complete `<indexterm>` support, with tests

Co-authored-by: Rowan Rodrik van der Molen <rowan@ytec.nl>

2 files changed, 199 insertions, 0 deletions

diff --git a/test/docbook-reader.docbook b/test/docbook-reader.docbook
index c38abda82..00bd84649 100644
--- a/test/docbook-reader.docbook
+++ b/test/docbook-reader.docbook
@@ -1603,4 +1603,16 @@ or here: <http://example.com/>
     </step>
   </procedure>
 </sect1>
+<sect1 id="indexterms">
+  <title>Index terms</title>
+  <para>
+    In the simplest case, index terms<indexterm><primary>index term</primary></indexterm> consists of just a <code>&lt;primary&gt;</code> element, but <indexterm><primary>index term</primary><secondary>multi-level</secondary></indexterm> they can also consist of a <code>&lt;primary&gt;</code> <emph>and</emph> <code>&lt;secondary&gt;</code> element, and <indexterm><primary>index term</primary><secondary>multi-level</secondary><tertiary>3-level</tertiary></indexterm> can even include a <code>&lt;tertiary&gt;</code> term.
+  </para>
+  <para>
+    Index terms can also refer to other index terms: <indexterm><primary>index cross referencing</primary></indexterm><indexterm><primary>index term</primary><secondary>cross references</secondary><see>index cross referencing</see></indexterm>exclusively, using the <code>&lt;see&gt;</code> tag; or <indexterm><primary>index cross referencing</primary><seealso>cross referencing</seealso></indexterm> as a reference to related terms, using the <code>&lt;seealso&gt;</code> tag.
+  </para>
+  <para>
+    <indexterm><primary>food</primary><secondary>big <foreignphrase>baguette</foreignphrase> <strong>supreme</strong></secondary></indexterm>Nested content in index term elements is flattened.
+  </para>
+</sect1>
 </article>
diff --git a/test/docbook-reader.native b/test/docbook-reader.native
index be3819336..7520068b1 100644
--- a/test/docbook-reader.native
+++ b/test/docbook-reader.native
@@ -2930,4 +2930,191 @@ Pandoc
             [ Str "A" , Space , Str "Final" , Space , Str "Step" ]
         ]
       ]
+  , Header
+      1
+      ( "indexterms" , [] , [] )
+      [ Str "Index" , Space , Str "terms" ]
+  , Para
+      [ Str "In"
+      , Space
+      , Str "the"
+      , Space
+      , Str "simplest"
+      , Space
+      , Str "case,"
+      , Space
+      , Str "index"
+      , Space
+      , Str "terms"
+      , Span
+          ( "" , [ "indexterm" ] , [ ( "primary" , "index term" ) ] )
+          []
+      , Space
+      , Str "consists"
+      , Space
+      , Str "of"
+      , Space
+      , Str "just"
+      , Space
+      , Str "a"
+      , Space
+      , Code ( "" , [] , [] ) "<primary>"
+      , Space
+      , Str "element,"
+      , Space
+      , Str "but"
+      , Space
+      , Span
+          ( ""
+          , [ "indexterm" ]
+          , [ ( "primary" , "index term" )
+            , ( "secondary" , "multi-level" )
+            ]
+          )
+          []
+      , Space
+      , Str "they"
+      , Space
+      , Str "can"
+      , Space
+      , Str "also"
+      , Space
+      , Str "consist"
+      , Space
+      , Str "of"
+      , Space
+      , Str "a"
+      , Space
+      , Code ( "" , [] , [] ) "<primary>"
+      , Space
+      , Str "and"
+      , Space
+      , Code ( "" , [] , [] ) "<secondary>"
+      , Space
+      , Str "element,"
+      , Space
+      , Str "and"
+      , Space
+      , Span
+          ( ""
+          , [ "indexterm" ]
+          , [ ( "primary" , "index term" )
+            , ( "secondary" , "multi-level" )
+            , ( "tertiary" , "3-level" )
+            ]
+          )
+          []
+      , Space
+      , Str "can"
+      , Space
+      , Str "even"
+      , Space
+      , Str "include"
+      , Space
+      , Str "a"
+      , Space
+      , Code ( "" , [] , [] ) "<tertiary>"
+      , Space
+      , Str "term."
+      ]
+  , Para
+      [ Str "Index"
+      , Space
+      , Str "terms"
+      , Space
+      , Str "can"
+      , Space
+      , Str "also"
+      , Space
+      , Str "refer"
+      , Space
+      , Str "to"
+      , Space
+      , Str "other"
+      , Space
+      , Str "index"
+      , Space
+      , Str "terms:"
+      , Space
+      , Span
+          ( ""
+          , [ "indexterm" ]
+          , [ ( "primary" , "index cross referencing" ) ]
+          )
+          []
+      , Span
+          ( ""
+          , [ "indexterm" ]
+          , [ ( "primary" , "index term" )
+            , ( "secondary" , "cross references" )
+            , ( "see" , "index cross referencing" )
+            ]
+          )
+          []
+      , Str "exclusively,"
+      , Space
+      , Str "using"
+      , Space
+      , Str "the"
+      , Space
+      , Code ( "" , [] , [] ) "<see>"
+      , Space
+      , Str "tag;"
+      , Space
+      , Str "or"
+      , Space
+      , Span
+          ( ""
+          , [ "indexterm" ]
+          , [ ( "primary" , "index cross referencing" )
+            , ( "seealso" , "cross referencing" )
+            ]
+          )
+          []
+      , Space
+      , Str "as"
+      , Space
+      , Str "a"
+      , Space
+      , Str "reference"
+      , Space
+      , Str "to"
+      , Space
+      , Str "related"
+      , Space
+      , Str "terms,"
+      , Space
+      , Str "using"
+      , Space
+      , Str "the"
+      , Space
+      , Code ( "" , [] , [] ) "<seealso>"
+      , Space
+      , Str "tag."
+      ]
+  , Para
+      [ Span
+          ( ""
+          , [ "indexterm" ]
+          , [ ( "primary" , "food" )
+            , ( "secondary" , "big baguette supreme" )
+            ]
+          )
+          []
+      , Str "Nested"
+      , Space
+      , Str "content"
+      , Space
+      , Str "in"
+      , Space
+      , Str "index"
+      , Space
+      , Str "term"
+      , Space
+      , Str "elements"
+      , Space
+      , Str "is"
+      , Space
+      , Str "flattened."
+      ]
   ]