document the index_columns key in the theming guide [skip ci]

1 files changed, 18 insertions, 0 deletions

diff --git a/docs/theming-guide.adoc b/docs/theming-guide.adoc
index 8ea09df2..7ba83e53 100644
--- a/docs/theming-guide.adoc
+++ b/docs/theming-guide.adoc
@@ -4403,6 +4403,24 @@ Permitted attribute values are even, odd, all, and none.
 Prior to Asciidoctor 2, even rows are shaded by default (e.g., `stripes=even`).
 Since Asciidoctor 2, table stripes are not enabled by default (e.g., `stripes=none`).
 
+[#keys-index]
+=== Index
+
+The keys in this category control the style of the autogenerated index section.
+
+[cols="3,4,5l"]
+|===
+|Key |Value Type |Example
+
+3+|[#key-prefix-index]*Key Prefix:* <<key-prefix-index,index>>
+
+|columns
+|Integer +
+(default: 2)
+|index:
+  columns: 2
+|===
+
 [#keys-footnotes]
 === Footnotes