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-rw-r--r--doc/lua-filters.md37
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diff --git a/doc/lua-filters.md b/doc/lua-filters.md
index 145a1517f..34165a791 100644
--- a/doc/lua-filters.md
+++ b/doc/lua-filters.md
@@ -107,3 +107,40 @@ return {
end,
}
```
+
+### Extracting information about links
+
+This filter prints a table of all the URLs linked to
+in the document, together with the number of links to
+that URL.
+
+```lua
+links = {}
+
+function Link (el)
+ if links[el.target] then
+ links[el.target] = links[el.target] + 1
+ else
+ links[el.target] = 1
+ end
+ return el
+end
+
+function Doc (blocks, meta)
+ function strCell(str)
+ return {pandoc.Plain{pandoc.Str(str)}}
+ end
+ local caption = {pandoc.Str "Link", pandoc.Space(), pandoc.Str "count"}
+ local aligns = {pandoc.AlignDefault, pandoc.AlignLeft}
+ local widths = {0.8, 0.2}
+ local headers = {strCell "Target", strCell "Count"}
+ local rows = {}
+ for link, count in pairs(links) do
+ rows[#rows + 1] = {strCell(link), strCell(count)}
+ end
+ return pandoc.Doc(
+ {pandoc.Table(caption, aligns, widths, headers, rows)},
+ meta
+ )
+end
+```