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[Filter] add rewritelinks filter: transform image src and link targets in markdown files (recursively) (#116)
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‎filters/hugo_rewritelinks.lua‎

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--[[
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All 'readme.md' will be transformed into '_index.md', any other Markdown file
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'file.md' will be transformed into 'file/_index.md' (see 'hugo_makedeps.lua').
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This filter will adapt the image sources and the link targets in a Markdown
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file so that Hugo can build a web page from it.
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]]--
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-- local vars
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local INDEX_MD = "readme" -- name of readme.md (will be set from metadata)
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-- helper
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local function _is_relative (target)
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return pandoc.path.is_relative(target)
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end
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local function _is_markdown (target)
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return target:match('.*%.md')
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end
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local function _is_url (target)
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return target:match('https?://.*')
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end
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-- replace `![](img/b.png)` with `![](b.png)`
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function Image (image)
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if _is_relative(image.src) and not _is_url(image.src) then
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image.src = pandoc.path.filename(image.src)
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return image
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end
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end
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--[[
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Hugo's ref shortcode tries to resolve paths without a leading '/' first relative to the current page,
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then to the rest of the site. As long as all pages have a _unique name_, we can also simply use the
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name of the page. Index pages ('_index.md') must be referenced via their toplevel folder.
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All files will be transformed during processing (see 'hugo_makedeps.lua'):
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- 'subdir/file-a.md' will become 'subdir/file-a/_index.md'
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- 'subdir/readme.md' will become 'subdir/_index.md'
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Since "subdir" might contain something like "../", we would have to resolve this first. However, as
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Hugo's ref shortcode can also resolve just the filename without a path, we can skip this effort and
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just replace the path with the filename. For index files ('readme.md'), we have to extract the last
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folder.
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This filter need to perform for any link in any Markdown file:
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- replace `[Y](subdir/file-a.md)` with `[Y]({{< ref "file-a" >}})`
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- replace `[Y](subdir/readme.md)` with `[Y]({{< ref "subdir" >}})`
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- replace `[Y](readme.md)` with `[Y]({{< ref "/" >}})` (might work with Hugo)
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Caveats:
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(a) All referenced Markdown files must have UNIQUE NAMES.
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(b) References to the top index page (landing page) are (presumably) not working.
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]]--
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function Link (link)
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local target = link.target
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local content = pandoc.utils.stringify(link.content)
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if _is_markdown(target) and _is_relative(target) and not _is_url(target) then
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local dir = pandoc.path.split(pandoc.path.directory(target)) -- 'foo.md' => {'.'}; 'sub/foo.md' => {'sub'}; './sub/foo.md' => {'.', 'sub'};
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local name, _ = pandoc.path.split_extension(pandoc.path.filename(target))
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if name == INDEX_MD then
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target = (#dir >= 1 and dir[#dir] ~= ".") and dir[#dir] or "/" -- readme.md: use parent folder or '/'
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else
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target = name -- ordinary file: use it's name w/o extension
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end
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return pandoc.RawInline('markdown', '[' .. content .. ']({{< ref "' .. target .. '" >}})')
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end
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end
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function Meta (m)
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INDEX_MD = m.indexMD or "readme"
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end
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return {
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{ Meta = Meta },
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{ Image = Image },
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{ Link = Link }
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}

‎filters/test filter/Makefile‎

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DIFF ?= diff --strip-trailing-cr -u
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PANDOC ?= pandoc
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FILES_TRANSFORM = readme.md
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FILES_MAKEDEPS = readme.md
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LUA_REWRITELINKS = ../hugo_rewritelinks.lua
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LUA_MAKEDEPS = ../hugo_makedeps.lua
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test: test_makedeps
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test: test_rewritelinks test_makedeps
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test_rewritelinks: $(FILES_TRANSFORM)
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@$(PANDOC) -L $(LUA_REWRITELINKS) -t native $^ \
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| $(DIFF) expected_rewritelinks1.native -
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@$(PANDOC) -L $(LUA_REWRITELINKS) -M indexMD="foo" -t native $^ \
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| $(DIFF) expected_rewritelinks2.native -
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@$(PANDOC) -L $(LUA_REWRITELINKS) -M indexMD="readme" -t native $^ \
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| $(DIFF) expected_rewritelinks3.native -
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@$(PANDOC) -L $(LUA_REWRITELINKS) -M weight=42 -M indexMD="readme" -t native $^ \
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| $(DIFF) expected_rewritelinks4.native -
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test_makedeps: $(FILES_MAKEDEPS)
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@$(PANDOC) -L $(LUA_MAKEDEPS) -t native $^ \
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| $(DIFF) expected_makedeps4.native -
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expected: expected_rewritelinks1.native expected_rewritelinks2.native expected_rewritelinks3.native expected_rewritelinks4.native
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expected_rewritelinks1.native: $(FILES_TRANSFORM)
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$(PANDOC) -L $(LUA_REWRITELINKS) -t native -o $@ $^
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expected_rewritelinks2.native: $(FILES_TRANSFORM)
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$(PANDOC) -L $(LUA_REWRITELINKS) -M indexMD="foo" -t native -o $@ $^
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expected_rewritelinks3.native: $(FILES_TRANSFORM)
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$(PANDOC) -L $(LUA_REWRITELINKS) -M indexMD="readme" -t native -o $@ $^
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expected_rewritelinks4.native: $(FILES_TRANSFORM)
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$(PANDOC) -L $(LUA_REWRITELINKS) -M weight=42 -M indexMD="readme" -t native -o $@ $^
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expected: expected_makedeps1.native expected_makedeps2.native expected_makedeps3.native expected_makedeps4.native
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expected_makedeps1.native: $(FILES_MAKEDEPS)
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$(PANDOC) -L $(LUA_MAKEDEPS) -t native -o $@ $^
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clean:
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rm -rf expected_rewritelinks1.native expected_rewritelinks2.native expected_rewritelinks3.native expected_rewritelinks4.native
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rm -rf expected_makedeps1.native expected_makedeps2.native expected_makedeps3.native expected_makedeps4.native
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36-
.PHONY: test test_makedeps expected clean
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.PHONY: test test_rewritelinks test_makedeps expected clean

‎filters/test filter/expected_rewritelinks1.native‎

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[ Header 1 ( "summary.md" , [] , [] ) [ Str "Summary.md" ]
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, Header
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2
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( "this-should-work" , [] , [] )
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[ Str "This" , Space , Str "should" , Space , Str "work" ]
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, Para [ Str "Thanks" , Space , Str "everyone!" ]
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, Para
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[ RawInline
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(Format "markdown") "[File A]({{< ref \"file-a\" >}})"
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]
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, Para
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[ RawInline
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(Format "markdown") "[File A]({{< ref \"file-a\" >}})"
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]
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, Figure
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( "" , [] , [] )
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(Caption
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Nothing
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[ Plain
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[ Str "Image"
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, Space
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, Str "A"
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, Space
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, Str "(from"
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, Space
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, Str "Readme.md)"
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]
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])
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[ Plain
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[ Image
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( "" , [] , [] )
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[ Str "Image"
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, Space
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, Str "A"
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, Space
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, Str "(from"
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, Space
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, Str "Readme.md)"
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]
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( "a.png" , "" )
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]
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]
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, Para [ Image ( "" , [] , [] ) [] ( "a.png" , "" ) ]
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, Header
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2
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( "different-wrong-format" , [] , [] )
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[ Str "Different"
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, Space
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, Str "(wrong)"
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, Space
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, Str "format"
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]
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, BulletList
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[ [ Plain
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[ Link
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( "" , [] , [] )
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[ Str "wrong" , Space , Str "extension" ]
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( "file-c.png" , "" )
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]
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]
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, [ Plain
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[ Link
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( "" , [] , [] )
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[ Str "not" , Space , Str "local" ]
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( "https://pandoc.org/lua-filters.html" , "" )
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]
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]
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, [ Plain
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[ Link
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( "" , [] , [] )
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[ Str "still" , Space , Str "not" , Space , Str "local" ]
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( "https://pandoc.org/lua-filters.md" , "" )
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]
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]
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, [ Plain
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[ Link
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( "" , [] , [] )
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[ Str "also" , Space , Str "not" , Space , Str "local" ]
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( "http://pandoc.org/lua-filters.md" , "" )
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]
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]
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, [ Plain
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[ RawInline
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(Format "markdown")
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"[not there and not here]({{< ref \"wuppie\" >}})"
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]
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]
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]
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, Header
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2
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( "recursive-inclusion" , [] , [] )
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[ Str "Recursive" , Space , Str "inclusion" ]
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, Para
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[ RawInline
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(Format "markdown") "[File B]({{< ref \"file-b\" >}})"
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]
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, Header
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2 ( "subdirectories" , [] , [] ) [ Str "Subdirectories" ]
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, Para
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[ RawInline
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(Format "markdown")
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"[Subdir: File D]({{< ref \"file-d\" >}})"
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]
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, Para
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[ RawInline
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(Format "markdown")
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"[Subdir: File D]({{< ref \"file-d\" >}})"
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]
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, Header
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2
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( "subdirectories-recursive" , [] , [] )
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[ Str "Subdirectories," , Space , Str "recursive" ]
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, Para
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[ RawInline
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(Format "markdown")
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"[Subdir: File E]({{< ref \"file-e\" >}})"
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]
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, Header
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2
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( "subdirectories-direct-plus-recursive" , [] , [] )
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[ Str "Subdirectories,"
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, Space
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, Str "direct"
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, Space
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, Str "plus"
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, Space
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, Str "recursive"
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]
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, Para
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[ RawInline
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(Format "markdown")
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"[Subdir/Leaf: Foo]({{< ref \"foo\" >}})"
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]
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, Header
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2
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( "links-to-landing-pages" , [] , [] )
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[ Str "Links"
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, Space
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, Str "to"
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, Space
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, Str "Landing"
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, Space
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, Str "Pages"
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]
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, Para
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[ RawInline
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(Format "markdown")
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"[subdir/readme]({{< ref \"subdir\" >}})"
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]
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, Para
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[ RawInline
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(Format "markdown") "[readme]({{< ref \"/\" >}})"
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]
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]

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