Moved some details to a function

... regarding [attribute=value] and other matching.
Also explained (in comments) the different matching patterns.
And fixed a bug where /> would be listed as an attribute.
And added a few more tests.

ElementNode.lua

@@ -89,12 +89,34 @@ end
 
 local function select(self, s)
   if not s or type(s) ~= "string" or s == "" then return Set:new() end
-  local sets = {
-    [""]  = self.deeperelements,
-    ["["] = self.deeperattributes,
-    ["#"] = self.deeperids,
-    ["."] = self.deeperclasses
-  }
+
+  local function match(t, w)
+    local sets = {
+      [""]  = self.deeperelements,
+      ["["] = self.deeperattributes,
+      ["#"] = self.deeperids,
+      ["."] = self.deeperclasses
+    }
+    local v
+    if t == "[" then
+      w, v = string.match(w, 
+        "([^=]+)" .. -- w = 1 or more characters up to a possible "="
+        "=?" ..      -- an optional uncaptured "="
+        "(.*)"      -- v = anything following the "=", or else ""
+      )
+    end
+    local matched = sets[t][w]
+    if v and v ~= "" then
+      v = string.sub(v, 2, #v - 1) -- strip quotes
+      for node in pairs(matched) do
+        if node.attributes[w] ~= v then
+          matched:remove(node)
+        end
+      end
+    end
+    return matched
+  end
+
   local subjects, resultset, childrenonly = Set:new({self})
   for part in string.gmatch(s, "%S+") do
     if part == ">" then childrenonly = true goto nextpart end
@@ -107,28 +129,17 @@ local function select(self, s)
     end
     if part == "*" then goto nextpart end
     local excludes, filter = Set:new()
-    for t, w, v in string.gmatch(part,
+    for t, w in string.gmatch(part,
       "([:%[#.]?)" ..        -- t = an optional :, [, #, or .
       "([^:%(%[#.%]%)]+)" .. -- w = 1 or more of anything not :, (, [, #, ., ], or )
       "%]?%)?"               -- followed by an uncaptured optional ] and/or )
     ) do
       if t == ":" then filter = w goto nextw end
-      if t == "[" then
-        w, v = string.match(w, "([^=]+)=?(%S*)")
-      end
-      local match = sets[t][w]
-      if v and v ~= "" then
-        v = string.sub(v, 2, #v - 1) -- strip quotes
-        for node in pairs(match) do
-          if node.attributes[w] ~= v then
-            match:remove(node)
-          end
-        end
-      end
+      local matched = match(t, w)
       if filter == "not" then
-        excludes = excludes + match
+        excludes = excludes + matched
       else
-        resultset = resultset * match
+        resultset = resultset * matched
       end
       filter = nil
       ::nextw::

htmlparser.lua

@@ -9,7 +9,11 @@ local function parse(text)
   local node, descend, tpos, opentags = root, true, 1, {}
   while true do
     local openstart, name
-    openstart, tpos, name = string.find(root._text, "<(%w+)[^>]*>", tpos)
+    openstart, tpos, name = string.find(root._text, 
+      "<" ..     -- an uncaptured starting "<"
+      "(%w+)" .. -- name = the first word, directly following the "<"
+      "[^>]*>",  -- include, but not capture everything up to the next ">"
+    tpos)
     if not name then break end
     local tag = ElementNode:new(name, node, descend, openstart, tpos)
     node = tag
@@ -17,12 +21,17 @@ local function parse(text)
     local tagst, apos = tag:gettext(), 1
     while true do
       local start, k, eq, quote, v
-      start, apos, k, eq, quote = string.find(tagst, "%s+([^%s=]+)(=?)(['\"]?)", apos)
-      if not k then break end
+      start, apos, k, eq, quote = string.find(tagst, 
+        "%s+" ..       -- some uncaptured space
+        "([^%s=]+)" .. -- k = an unspaced string up to an optional "="
+        "(=?)" ..      -- eq = the optiona; "=", else ""
+        "(['\"]?)",    -- quote = an optional "'" or '"' following the "=", or ""
+      apos)
+      if not k or k == "/>" then break end
       if eq == "" then
         v = ""
       else
-        local pattern = "=([^%s'\">]*)"
+        local pattern = "=([^%s>]*)"
         if quote ~= '' then
           pattern = quote .. "([^" .. quote .. "]*)" .. quote
         end

test.html

@@ -1,5 +1,5 @@
 <!DOCTYPE html>
-<html lang="en" test1='val1' test2="val='2'" test3='val="3"' test4="val = 4" test5=val5>
+<html lang="en" test1='val1' test2="val='2'" test3='val="3"' test4="val = 4" test5=val5 test6=val""6>
 <head>
   <meta charset="utf-8" />
   <link rel="stylesheet" href="test.css" />

test.lua

@@ -10,11 +10,8 @@ local root = htmlparser.parse(text)
 local function p(n)
   local space = string.rep("  ", n.level)
   local s = space .. n.name
-  for i,v in ipairs(n.nodes) do
-    s = s .. " nodes[" .. i .. "]=" .. v.name
-  end
   for k,v in pairs(n.attributes) do
-    s = s .. " " .. k .. "=[" .. v .. "]"
+    s = s .. " " .. k .. "=[[" .. v .. "]]"
   end
   print(s)
   for i,v in ipairs(n.nodes) do
@@ -57,6 +54,11 @@ select("[itemscope]:not([itemprop])")
 
 select("link[rel='alternate']")
 select("[test2=\"val='2'\"]")
+select("[test5='val5']")
+select("[test6='val\"\"6']")
+select("[itemscope='']")
+select("[itemscope=]")
+select("[itemscope]")
 
 print("\nchapters")
 local sel, chapters = root("ol.chapters > li"), {}