Sgml.ContentModel.PushGroup C# (CSharp) Method

        public void PushGroup()
        {
            m_model = new Group(m_model);
            m_currentDepth++;
        }

        void ParseModel(char cmt, ContentModel cm)
        {
            // Called when part of the model is made up of the contents of a parameter entity
            int depth = cm.CurrentDepth;
            char ch = this.m_current.Lastchar;
            ch = this.m_current.SkipWhitespace();
            while (ch != cmt || cm.CurrentDepth > depth) // the entity must terminate while inside the content model.
            {
                if (ch == Entity.EOF) 
                {
                    this.m_current.Error("Content Model was not closed");
                }
                if (ch == '%') 
                {
                    Entity e = ParseParameterEntity(SgmlDtd.cmterm);
                    PushEntity(this.m_current.ResolvedUri, e);
                    ParseModel(Entity.EOF, cm);
                    PopEntity();                    
                    ch = this.m_current.SkipWhitespace();
                } 
                else if (ch == '(') 
                {
                    cm.PushGroup();
                    this.m_current.ReadChar();// consume '('
                    ch = this.m_current.SkipWhitespace();
                }
                else if (ch == ')') 
                {
                    ch = this.m_current.ReadChar();// consume ')'
                    if (ch == '*' || ch == '+' || ch == '?') 
                    {
                        cm.AddOccurrence(ch);
                        ch = this.m_current.ReadChar();
                    }
                    if (cm.PopGroup() < depth)
                    {
                        this.m_current.Error("Parameter entity cannot close a paren outside it's own scope");
                    }
                    ch = this.m_current.SkipWhitespace();
                }
                else if (ch == ',' || ch == '|' || ch == '&') 
                {
                    cm.AddConnector(ch);
                    this.m_current.ReadChar(); // skip connector
                    ch = this.m_current.SkipWhitespace();
                }
                else
                {
                    string token;
                    if (ch == '#') 
                    {
                        ch = this.m_current.ReadChar();
                        token = "#" + this.m_current.ScanToken(this.m_sb, SgmlDtd.cmterm, true); // since '#' is not a valid name character.
                    } 
                    else 
                    {
                        token = this.m_current.ScanToken(this.m_sb, SgmlDtd.cmterm, true);
                    }

                    token = token.ToUpperInvariant();
                    ch = this.m_current.Lastchar;
                    if (ch == '?' || ch == '+' || ch == '*') 
                    {
                        cm.PushGroup();
                        cm.AddSymbol(token);
                        cm.AddOccurrence(ch);
                        cm.PopGroup();
                        this.m_current.ReadChar(); // skip connector
                        ch = this.m_current.SkipWhitespace();
                    } 
                    else 
                    {
                        cm.AddSymbol(token);
                        ch = this.m_current.SkipWhitespace();
                    }                   
                }
            }
        }