diff --git a/spec/imbecile/regex/parser_spec.rb b/spec/imbecile/regex/parser_spec.rb
index d9672e1..2092386 100644
--- a/spec/imbecile/regex/parser_spec.rb
+++ b/spec/imbecile/regex/parser_spec.rb
@@ -2,8 +2,320 @@ module Imbecile
   class Regex
     RSpec.describe Parser do
 
-      it "parses various expressions" do
-        expect(Parser.new("").unit).to be_a Parser::AlternatesUnit
+      it "parses an empty expression" do
+        parser = Parser.new("")
+        expect(parser.unit).to be_a Parser::AlternatesUnit
+        expect(parser.unit.alternates.size).to eq 0
+      end
+
+      it "parses a single character unit expression" do
+        parser = Parser.new("a")
+        expect(parser.unit).to be_a Parser::AlternatesUnit
+        expect(parser.unit.alternates.size).to eq 1
+        expect(parser.unit.alternates[0]).to be_a Parser::SequenceUnit
+        seq_unit = parser.unit.alternates[0]
+        expect(seq_unit.size).to eq 1
+        expect(seq_unit[0]).to be_a Parser::CharacterUnit
+      end
+
+      it "parses a group with a single character unit expression" do
+        parser = Parser.new("(a)")
+        expect(parser.unit).to be_a Parser::AlternatesUnit
+        expect(parser.unit.alternates.size).to eq 1
+        expect(parser.unit.alternates[0]).to be_a Parser::SequenceUnit
+        seq_unit = parser.unit.alternates[0]
+        expect(seq_unit.size).to eq 1
+        expect(seq_unit[0]).to be_a Parser::AlternatesUnit
+        alt_unit = seq_unit[0]
+        expect(alt_unit.alternates.size).to eq 1
+        expect(alt_unit.alternates[0]).to be_a Parser::SequenceUnit
+        expect(alt_unit.alternates[0][0]).to be_a Parser::CharacterUnit
+      end
+
+      it "parses a *" do
+        parser = Parser.new("a*")
+        expect(parser.unit).to be_a Parser::AlternatesUnit
+        expect(parser.unit.alternates.size).to eq 1
+        expect(parser.unit.alternates[0]).to be_a Parser::SequenceUnit
+        seq_unit = parser.unit.alternates[0]
+        expect(seq_unit.size).to eq 1
+        expect(seq_unit[0]).to be_a Parser::MultiplicityUnit
+        m_unit = seq_unit[0]
+        expect(m_unit.min_count).to eq 0
+        expect(m_unit.max_count).to be_nil
+        expect(m_unit.unit).to be_a Parser::CharacterUnit
+      end
+
+      it "parses a +" do
+        parser = Parser.new("a+")
+        expect(parser.unit).to be_a Parser::AlternatesUnit
+        expect(parser.unit.alternates.size).to eq 1
+        expect(parser.unit.alternates[0]).to be_a Parser::SequenceUnit
+        seq_unit = parser.unit.alternates[0]
+        expect(seq_unit.size).to eq 1
+        expect(seq_unit[0]).to be_a Parser::MultiplicityUnit
+        m_unit = seq_unit[0]
+        expect(m_unit.min_count).to eq 1
+        expect(m_unit.max_count).to be_nil
+        expect(m_unit.unit).to be_a Parser::CharacterUnit
+      end
+
+      it "parses a ?" do
+        parser = Parser.new("a?")
+        expect(parser.unit).to be_a Parser::AlternatesUnit
+        expect(parser.unit.alternates.size).to eq 1
+        expect(parser.unit.alternates[0]).to be_a Parser::SequenceUnit
+        seq_unit = parser.unit.alternates[0]
+        expect(seq_unit.size).to eq 1
+        expect(seq_unit[0]).to be_a Parser::MultiplicityUnit
+        m_unit = seq_unit[0]
+        expect(m_unit.min_count).to eq 0
+        expect(m_unit.max_count).to eq 1
+        expect(m_unit.unit).to be_a Parser::CharacterUnit
+      end
+
+      it "parses a multiplicity count" do
+        parser = Parser.new("a{5}")
+        expect(parser.unit).to be_a Parser::AlternatesUnit
+        expect(parser.unit.alternates.size).to eq 1
+        expect(parser.unit.alternates[0]).to be_a Parser::SequenceUnit
+        seq_unit = parser.unit.alternates[0]
+        expect(seq_unit.size).to eq 1
+        expect(seq_unit[0]).to be_a Parser::MultiplicityUnit
+        m_unit = seq_unit[0]
+        expect(m_unit.min_count).to eq 5
+        expect(m_unit.max_count).to eq 5
+        expect(m_unit.unit).to be_a Parser::CharacterUnit
+      end
+
+      it "parses a minimum-only multiplicity count" do
+        parser = Parser.new("a{5,}")
+        expect(parser.unit).to be_a Parser::AlternatesUnit
+        expect(parser.unit.alternates.size).to eq 1
+        expect(parser.unit.alternates[0]).to be_a Parser::SequenceUnit
+        seq_unit = parser.unit.alternates[0]
+        expect(seq_unit.size).to eq 1
+        expect(seq_unit[0]).to be_a Parser::MultiplicityUnit
+        m_unit = seq_unit[0]
+        expect(m_unit.min_count).to eq 5
+        expect(m_unit.max_count).to be_nil
+        expect(m_unit.unit).to be_a Parser::CharacterUnit
+      end
+
+      it "parses a minimum and maximum multiplicity count" do
+        parser = Parser.new("a{5,8}")
+        expect(parser.unit).to be_a Parser::AlternatesUnit
+        expect(parser.unit.alternates.size).to eq 1
+        expect(parser.unit.alternates[0]).to be_a Parser::SequenceUnit
+        seq_unit = parser.unit.alternates[0]
+        expect(seq_unit.size).to eq 1
+        expect(seq_unit[0]).to be_a Parser::MultiplicityUnit
+        m_unit = seq_unit[0]
+        expect(m_unit.min_count).to eq 5
+        expect(m_unit.max_count).to eq 8
+        expect(m_unit.unit).to be_a Parser::CharacterUnit
+        expect(m_unit.unit.code_point).to eq "a".ord
+      end
+
+      it "parses an escaped *" do
+        parser = Parser.new("a\\*")
+        expect(parser.unit).to be_a Parser::AlternatesUnit
+        expect(parser.unit.alternates.size).to eq 1
+        expect(parser.unit.alternates[0]).to be_a Parser::SequenceUnit
+        seq_unit = parser.unit.alternates[0]
+        expect(seq_unit.size).to eq 2
+        expect(seq_unit[0]).to be_a Parser::CharacterUnit
+        expect(seq_unit[0].code_point).to eq "a".ord
+        expect(seq_unit[1]).to be_a Parser::CharacterUnit
+        expect(seq_unit[1].code_point).to eq "*".ord
+      end
+
+      it "parses an escaped +" do
+        parser = Parser.new("a\\+")
+        expect(parser.unit).to be_a Parser::AlternatesUnit
+        expect(parser.unit.alternates.size).to eq 1
+        expect(parser.unit.alternates[0]).to be_a Parser::SequenceUnit
+        seq_unit = parser.unit.alternates[0]
+        expect(seq_unit.size).to eq 2
+        expect(seq_unit[0]).to be_a Parser::CharacterUnit
+        expect(seq_unit[0].code_point).to eq "a".ord
+        expect(seq_unit[1]).to be_a Parser::CharacterUnit
+        expect(seq_unit[1].code_point).to eq "+".ord
+      end
+
+      it "parses an escaped \\" do
+        parser = Parser.new("\\\\d")
+        expect(parser.unit).to be_a Parser::AlternatesUnit
+        expect(parser.unit.alternates.size).to eq 1
+        expect(parser.unit.alternates[0]).to be_a Parser::SequenceUnit
+        seq_unit = parser.unit.alternates[0]
+        expect(seq_unit.size).to eq 2
+        expect(seq_unit[0]).to be_a Parser::CharacterUnit
+        expect(seq_unit[0].code_point).to eq "\\".ord
+        expect(seq_unit[1]).to be_a Parser::CharacterUnit
+        expect(seq_unit[1].code_point).to eq "d".ord
+      end
+
+      it "parses a character class" do
+        parser = Parser.new("[a-z_]")
+        expect(parser.unit).to be_a Parser::AlternatesUnit
+        expect(parser.unit.alternates.size).to eq 1
+        expect(parser.unit.alternates[0]).to be_a Parser::SequenceUnit
+        seq_unit = parser.unit.alternates[0]
+        expect(seq_unit.size).to eq 1
+        expect(seq_unit[0]).to be_a Parser::AlternatesUnit
+        alt_unit = seq_unit[0]
+        expect(alt_unit.negate).to be_falsey
+        expect(alt_unit.alternates.size).to eq 2
+        expect(alt_unit.alternates[0]).to be_a Parser::CharacterRangeUnit
+        expect(alt_unit.alternates[0].min_code_point).to eq "a".ord
+        expect(alt_unit.alternates[0].max_code_point).to eq "z".ord
+        expect(alt_unit.alternates[1]).to be_a Parser::CharacterUnit
+        expect(alt_unit.alternates[1].code_point).to eq "_".ord
+      end
+
+      it "parses a negated character class" do
+        parser = Parser.new("[^xyz]")
+        expect(parser.unit).to be_a Parser::AlternatesUnit
+        expect(parser.unit.alternates.size).to eq 1
+        expect(parser.unit.alternates[0]).to be_a Parser::SequenceUnit
+        seq_unit = parser.unit.alternates[0]
+        expect(seq_unit.size).to eq 1
+        expect(seq_unit[0]).to be_a Parser::AlternatesUnit
+        alt_unit = seq_unit[0]
+        expect(alt_unit.negate).to be_truthy
+        expect(alt_unit.alternates.size).to eq 3
+        expect(alt_unit.alternates[0]).to be_a Parser::CharacterUnit
+        expect(alt_unit.alternates[0].code_point).to eq "x".ord
+      end
+
+      it "parses - as a plain character at beginning of a character class" do
+        parser = Parser.new("[-9]")
+        expect(parser.unit).to be_a Parser::AlternatesUnit
+        expect(parser.unit.alternates.size).to eq 1
+        expect(parser.unit.alternates[0]).to be_a Parser::SequenceUnit
+        seq_unit = parser.unit.alternates[0]
+        expect(seq_unit.size).to eq 1
+        expect(seq_unit[0]).to be_a Parser::AlternatesUnit
+        alt_unit = seq_unit[0]
+        expect(alt_unit.alternates.size).to eq 2
+        expect(alt_unit.alternates[0]).to be_a Parser::CharacterUnit
+        expect(alt_unit.alternates[0].code_point).to eq "-".ord
+      end
+
+      it "parses - as a plain character at end of a character class" do
+        parser = Parser.new("[0-]")
+        expect(parser.unit).to be_a Parser::AlternatesUnit
+        expect(parser.unit.alternates.size).to eq 1
+        expect(parser.unit.alternates[0]).to be_a Parser::SequenceUnit
+        seq_unit = parser.unit.alternates[0]
+        expect(seq_unit.size).to eq 1
+        expect(seq_unit[0]).to be_a Parser::AlternatesUnit
+        alt_unit = seq_unit[0]
+        expect(alt_unit.alternates.size).to eq 2
+        expect(alt_unit.alternates[0]).to be_a Parser::CharacterUnit
+        expect(alt_unit.alternates[0].code_point).to eq "0".ord
+        expect(alt_unit.alternates[1]).to be_a Parser::CharacterUnit
+        expect(alt_unit.alternates[1].code_point).to eq "-".ord
+      end
+
+      it "parses - as a plain character at beginning of a negated character class" do
+        parser = Parser.new("[^-9]")
+        expect(parser.unit).to be_a Parser::AlternatesUnit
+        expect(parser.unit.alternates.size).to eq 1
+        expect(parser.unit.alternates[0]).to be_a Parser::SequenceUnit
+        seq_unit = parser.unit.alternates[0]
+        expect(seq_unit.size).to eq 1
+        expect(seq_unit[0]).to be_a Parser::AlternatesUnit
+        alt_unit = seq_unit[0]
+        expect(alt_unit.negate).to be_truthy
+        expect(alt_unit.alternates.size).to eq 2
+        expect(alt_unit.alternates[0]).to be_a Parser::CharacterUnit
+        expect(alt_unit.alternates[0].code_point).to eq "-".ord
+      end
+
+      it "parses . as a plain character in a negated character class" do
+        parser = Parser.new("[.]")
+        expect(parser.unit).to be_a Parser::AlternatesUnit
+        expect(parser.unit.alternates.size).to eq 1
+        expect(parser.unit.alternates[0]).to be_a Parser::SequenceUnit
+        seq_unit = parser.unit.alternates[0]
+        expect(seq_unit.size).to eq 1
+        expect(seq_unit[0]).to be_a Parser::AlternatesUnit
+        alt_unit = seq_unit[0]
+        expect(alt_unit.negate).to be_falsey
+        expect(alt_unit.alternates.size).to eq 1
+        expect(alt_unit.alternates[0]).to be_a Parser::CharacterUnit
+        expect(alt_unit.alternates[0].code_point).to eq ".".ord
+      end
+
+      it "parses - as a plain character when escaped in middle of character class" do
+        parser = Parser.new("[0\\-9]")
+        expect(parser.unit).to be_a Parser::AlternatesUnit
+        expect(parser.unit.alternates.size).to eq 1
+        expect(parser.unit.alternates[0]).to be_a Parser::SequenceUnit
+        seq_unit = parser.unit.alternates[0]
+        expect(seq_unit.size).to eq 1
+        expect(seq_unit[0]).to be_a Parser::AlternatesUnit
+        alt_unit = seq_unit[0]
+        expect(alt_unit.negate).to be_falsey
+        expect(alt_unit.alternates.size).to eq 3
+        expect(alt_unit.alternates[0]).to be_a Parser::CharacterUnit
+        expect(alt_unit.alternates[0].code_point).to eq "0".ord
+        expect(alt_unit.alternates[1]).to be_a Parser::CharacterUnit
+        expect(alt_unit.alternates[1].code_point).to eq "-".ord
+        expect(alt_unit.alternates[2]).to be_a Parser::CharacterUnit
+        expect(alt_unit.alternates[2].code_point).to eq "9".ord
+      end
+
+      it "parses alternates" do
+        parser = Parser.new("ab|c")
+        expect(parser.unit).to be_a Parser::AlternatesUnit
+        expect(parser.unit.alternates.size).to eq 2
+        expect(parser.unit.alternates[0]).to be_a Parser::SequenceUnit
+        expect(parser.unit.alternates[1]).to be_a Parser::SequenceUnit
+        expect(parser.unit.alternates[0].size).to eq 2
+        expect(parser.unit.alternates[1].size).to eq 1
+      end
+
+      it "parses something complex" do
+        parser = Parser.new("(a|)*|[^^]|\\|v|[x-y]+")
+        expect(parser.unit).to be_a Parser::AlternatesUnit
+        expect(parser.unit.alternates.size).to eq 4
+        expect(parser.unit.alternates[0]).to be_a Parser::SequenceUnit
+        expect(parser.unit.alternates[0].size).to eq 1
+        expect(parser.unit.alternates[0][0]).to be_a Parser::MultiplicityUnit
+        expect(parser.unit.alternates[0][0].min_count).to eq 0
+        expect(parser.unit.alternates[0][0].max_count).to be_nil
+        expect(parser.unit.alternates[0][0].unit).to be_a Parser::AlternatesUnit
+        expect(parser.unit.alternates[0][0].unit.alternates.size).to eq 2
+        expect(parser.unit.alternates[0][0].unit.alternates[0]).to be_a Parser::SequenceUnit
+        expect(parser.unit.alternates[0][0].unit.alternates[0].size).to eq 1
+        expect(parser.unit.alternates[0][0].unit.alternates[0][0]).to be_a Parser::CharacterUnit
+        expect(parser.unit.alternates[0][0].unit.alternates[1]).to be_a Parser::SequenceUnit
+        expect(parser.unit.alternates[0][0].unit.alternates[1].size).to eq 0
+        expect(parser.unit.alternates[1]).to be_a Parser::SequenceUnit
+        expect(parser.unit.alternates[1].size).to eq 1
+        expect(parser.unit.alternates[1][0]).to be_a Parser::AlternatesUnit
+        expect(parser.unit.alternates[1][0].negate).to be_truthy
+        expect(parser.unit.alternates[1][0].alternates.size).to eq 1
+        expect(parser.unit.alternates[1][0].alternates[0]).to be_a Parser::CharacterUnit
+        expect(parser.unit.alternates[2]).to be_a Parser::SequenceUnit
+        expect(parser.unit.alternates[2].size).to eq 2
+        expect(parser.unit.alternates[2][0]).to be_a Parser::CharacterUnit
+        expect(parser.unit.alternates[2][0].code_point).to eq "|".ord
+        expect(parser.unit.alternates[2][1]).to be_a Parser::CharacterUnit
+        expect(parser.unit.alternates[2][1].code_point).to eq "v".ord
+        expect(parser.unit.alternates[3]).to be_a Parser::SequenceUnit
+        expect(parser.unit.alternates[3].size).to eq 1
+        expect(parser.unit.alternates[3][0]).to be_a Parser::MultiplicityUnit
+        expect(parser.unit.alternates[3][0].min_count).to eq 1
+        expect(parser.unit.alternates[3][0].max_count).to be_nil
+        expect(parser.unit.alternates[3][0].unit).to be_a Parser::AlternatesUnit
+        expect(parser.unit.alternates[3][0].unit.alternates.size).to eq 1
+        expect(parser.unit.alternates[3][0].unit.alternates[0]).to be_a Parser::CharacterRangeUnit
+        expect(parser.unit.alternates[3][0].unit.alternates[0].min_code_point).to eq "x".ord
+        expect(parser.unit.alternates[3][0].unit.alternates[0].max_code_point).to eq "y".ord
       end
 
     end