HTML specific selector improvements (#140)

Ensure that all HTML specific selectors are comparing all related
elements against the XHTML namespace. In HTML parsers that do not
provide an HTML namespace for HTML elements, assume XHTML namespace.

Ensure that :root, :contains(), :lang(), :dir(), :default, and :indeterminate all consider
iframe boundaries and do not evaluate parent or child documents when
determining whether an element matches or not.

When a scoped selector is part of an iframe, :root should match that
scoped element's document root, and not the root of the whle tree.

Reference: #138

docs/src/markdown/about/changelog.md

@@ -1,5 +1,13 @@
 # Changelog
 
+## 1.9.1
+
+- **FIX**: `:root`, `:contains()`, `:default`, `:indeterminate`, `:lang()`, and `:dir()` will properly account for HTML
+`iframe` elements in their logic when selecting or matching an element. Their logic will be restricted to the document
+for which the element under consideration applies.
+- **FIX**: HTML pseudo-classes will check that all key elements checked are in the XHTML namespace (HTML parsers that do
+not provide namespaces will assume the XHTML namespace).
+
 ## 1.9.0
 
 - **NEW**: Allow `:contains()` to accept a list of text to search for. (#115)