diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 7eb055f..32255be 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -36,7 +36,7 @@ jobs:
       - name: Run tests
         run: ruby --version; bundle exec rspec spec || $ALLOW_FAILURES
       - name: Coveralls GitHub Action
-        uses: coverallsapp/github-action@v1.1.2
+        uses: coverallsapp/github-action@v2
         if: ${{ matrix.ruby == '3.0' && matrix.gemfile == 'Gemfile' }}
         with:
           github-token: ${{ secrets.GITHUB_TOKEN }}
diff --git a/lib/rdf/rdfa/reader/nokogiri.rb b/lib/rdf/rdfa/reader/nokogiri.rb
index 97d31d7..0f00bbd 100644
--- a/lib/rdf/rdfa/reader/nokogiri.rb
+++ b/lib/rdf/rdfa/reader/nokogiri.rb
@@ -35,8 +35,8 @@ def initialize(node, parent = nil)
         # @return [String]
         def language
           case
-          when @node.attribute_with_ns("lang", RDF::XML.to_s)
-            @node.attribute_with_ns("lang", RDF::XML.to_s)
+          when @node.attribute_with_ns("lang", "http://www.w3.org/XML/1998/namespace")
+            @node.attribute_with_ns("lang", "http://www.w3.org/XML/1998/namespace")
           when @node.attribute("xml:lang")
             @node.attribute("xml:lang").to_s
           when @node.attribute("lang")
@@ -49,7 +49,7 @@ def language
         #
         # @return [String]
         def base
-          @node.attribute_with_ns("base", RDF::XML.to_s) || @node.attribute('xml:base')
+          @node.attribute_with_ns("base", "http://www.w3.org/XML/1998/namespace") || @node.attribute('xml:base')
         end
 
         def display_path
@@ -303,7 +303,7 @@ def doc_base(base)
           base_el = @doc.at_css("html>head>base")
           base = base.join(base_el.attribute("href").to_s.split("#").first) if base_el
         else
-          xml_base = root.attribute_with_ns("base", RDF::XML.to_s) || root.attribute('xml:base') if root
+          xml_base = root.attribute_with_ns("base", "http://www.w3.org/XML/1998/namespace") || root.attribute('xml:base') if root
           base = base.join(xml_base) if xml_base
         end
 
diff --git a/lib/rdf/rdfa/reader/rexml.rb b/lib/rdf/rdfa/reader/rexml.rb
index a6f2753..60081a3 100644
--- a/lib/rdf/rdfa/reader/rexml.rb
+++ b/lib/rdf/rdfa/reader/rexml.rb
@@ -36,9 +36,9 @@ def initialize(node, parent = nil)
         #
         # @return [String]
         def language
-          language = case
-          when @node.attribute("lang", RDF::XML.to_s)
-            @node.attribute("lang", RDF::XML.to_s)
+          case
+          when @node.attribute("lang", "http://www.w3.org/XML/1998/namespace")
+            @node.attribute("lang", "http://www.w3.org/XML/1998/namespace")
           when @node.attribute("xml:lang")
             @node.attribute("xml:lang").to_s
           when @node.attribute("lang")
@@ -51,7 +51,7 @@ def language
         #
         # @return [String]
         def base
-          @node.attribute("base", RDF::XML.to_s) || @node.attribute('xml:base')
+          @node.attribute("base", "http://www.w3.org/XML/1998/namespace") || @node.attribute('xml:base')
         end
 
         def display_path
@@ -224,7 +224,7 @@ def initialize_xml(input, **options)
           @base_uri = base_uri ? base_uri.to_s : nil
 
           # Only parse as XML, no HTML mode
-          doc = ::REXML::Document.new(input.respond_to?(:read) ? input.read : input.to_s)
+          ::REXML::Document.new(input.respond_to?(:read) ? input.read : input.to_s)
         end
       end
 
@@ -331,7 +331,7 @@ def doc_base(base)
           base_el = ::REXML::XPath.first(@doc, "/html/head/base") rescue nil
           base = base.join(base_el.attribute("href").to_s.split("#").first) if base_el
         else
-          xml_base = root.attribute("base", RDF::XML.to_s) || root.attribute('xml:base') if root
+          xml_base = root.attribute("base", "http://www.w3.org/XML/1998/namespace") || root.attribute('xml:base') if root
           base = base.join(xml_base) if xml_base
         end
 
diff --git a/lib/rdf/rdfa/vocab.rb b/lib/rdf/rdfa/vocab.rb
index b2c2b94..bd3cc1d 100644
--- a/lib/rdf/rdfa/vocab.rb
+++ b/lib/rdf/rdfa/vocab.rb
@@ -155,7 +155,4 @@ module RDF
       "dc:description": "is the class for all warnings".freeze,
       subClassOf: "rdfa:PGClass".freeze
   end
-
-  XML = Class.new(Vocabulary("http://www.w3.org/XML/1998/namespace"))
-  XSI = Class.new(Vocabulary("http://www.w3.org/2001/XMLSchema-instance"))
 end