1 files changed, 85 insertions, 0 deletions
diff --git a/tex/context/base/strc-tag.lua b/tex/context/base/strc-tag.lua
new file mode 100644
index 000000000..4381fc529
--- /dev/null
+++ b/tex/context/base/strc-tag.lua
@@ -0,0 +1,85 @@
+if not modules then modules = { } end modules ['strc-tag'] = {
+    version   = 1.001,
+    comment   = "companion to strc-tag.mkiv",
+    author    = "Hans Hagen, PRAGMA-ADE, Hasselt NL",
+    copyright = "PRAGMA ADE / ConTeXt Development Team",
+    license   = "see context related readme files"
+}
+
+-- This is rather experimental code.
+
+local insert, remove, unpack, concat = table.insert, table.remove, table.unpack, table.concat
+local gsub, find, topattern, format = string.gsub, string.find, string.topattern, string.format
+local lpegmatch = lpeg.match
+local texattribute = tex.attribute
+local unsetvalue = attributes.unsetvalue
+
+structure.tags = structure.tags or { }
+
+local report_tags = logs.new("tags")
+
+local trace_tags = false  trackers.register("structure.tags", function(v) trace_tags = v end)
+
+local a_tagged = attributes.private('tagged')
+local a_image  = attributes.private('image')
+
+local tags, labels, stack, chain, ids, enabled = { }, { }, { }, { }, { }, false -- no grouping assumed
+
+structure.tags.taglist = tags -- can best be hidden
+
+function structure.tags.start(tag,label,detail)
+    labels[label or tag] = tag
+    if detail and detail ~= "" then
+        tag = tag .. ":" .. detail
+    end
+    if not enabled then
+        backends.codeinjections.enabletags(tags,labels)
+        enabled = true
+    end
+    local n = (ids[tag] or 0) + 1
+    ids[tag] = n
+    chain[#chain+1] = tag .. "-" .. n -- insert(chain,tag .. ":" .. n)
+    local t = #tags + 1
+    stack[#stack+1] = t -- insert(stack,t)
+    tags[t] = { unpack(chain) } -- we can add key values for alt and actualtext if needed
+    texattribute[a_tagged] = t
+    return t
+end
+
+function structure.tags.stop()
+    local t = stack[#stack] stack[#stack] = nil -- local t = remove(stack)
+    if not t then
+        if trace_tags then
+            report_tags("ignoring end tag, previous chain: %s",#chain > 0 and concat(chain[#chain]) or "none")
+        end
+        t = unsetvalue
+    else
+        chain[#chain] = nil -- remove(chain)
+    end
+    texattribute[a_tagged] = t
+    return t
+end
+
+function structure.atlocation(str)
+    local location = gsub(concat(tags[texattribute[a_tagged]],"-"),"%-%d+","")
+    return find(location,topattern(str)) ~= nil
+end
+
+function structure.tags.handler(head)  -- we need a dummy
+    return head, false
+end
+
+statistics.register("structure elements", function()
+    if enabled then
+        return format("%s element chains identified",#tags)
+    else
+        return nil
+    end
+end)
+
+directives.register("backend.addtags", function(v)
+    if not enabled then
+        backends.codeinjections.enabletags(tags,labels)
+        enabled = true
+    end
+end)