System.Xml.Schema.Asttree.CompileXPath C# (CSharp) Method

        public void CompileXPath (string xPath, bool isField, XmlNamespaceManager nsmgr) {
            if ((xPath == null) || (xPath.Length == 0)) {
                throw new XmlSchemaException(Res.Sch_EmptyXPath, string.Empty);
            }

            // firstly i still need to have an ArrayList to store tree only...
            // can't new ForwardAxis right away
            string[] xpath = xPath.Split('|');
            ArrayList AstArray = new ArrayList(xpath.Length);
            this.fAxisArray = new ArrayList(xpath.Length);

            // throw compile exceptions
            // can i only new one builder here then run compile several times??
            try {
                foreach (string value in xpath) {
                    // default ! isdesorself (no .//)
                    Axis ast = (Axis) (XPathParser.ParseXPathExpresion(value));
                    AstArray.Add (ast);
                }
            }   
            catch {
                throw  new XmlSchemaException(Res.Sch_ICXpathError, xPath);
            }

            Axis stepAst;
            foreach (Axis ast in AstArray) {
                // Restricted form
                // field can have an attribute:

                // throw exceptions during casting
                if ((stepAst = ast) == null) {
                    throw new XmlSchemaException(Res.Sch_ICXpathError, xPath);
                }

                Axis top = stepAst;

                // attribute will have namespace too
                // field can have top attribute
                if (IsAttribute (stepAst)) {
                    if (! isField) {
                        throw new XmlSchemaException(Res.Sch_SelectorAttr, xPath);
                    }
                    else {
                        SetURN (stepAst, nsmgr);
                        try {
                            stepAst = (Axis) (stepAst.Input);
                        }
                        catch {
                            throw new XmlSchemaException(Res.Sch_ICXpathError, xPath);
                        }
                    }
                }

                // field or selector
                while ((stepAst != null) && (IsNameTest (stepAst) || IsSelf (stepAst))) {
                    // trim tree "." node, if it's not the top one
                    if (IsSelf (stepAst) && (ast != stepAst)) {
                        top.Input = stepAst.Input;
                    }
                    else {
                        top = stepAst;
                        // set the URN
                        if (IsNameTest(stepAst)) {
                            SetURN (stepAst, nsmgr);
                        }
                    }
                    try {
                        stepAst = (Axis) (stepAst.Input);
                    }
                    catch {
                        throw new XmlSchemaException(Res.Sch_ICXpathError, xPath);
                    }
                }

                // the rest part can only be .// or null
                // trim the rest part, but need compile the rest part first
                top.Input = null;
                if (stepAst == null) {      // top "." and has other element beneath, trim this "." node too
                    if (IsSelf(ast) && (ast.Input != null)) {
                        this.fAxisArray.Add ( new ForwardAxis ( DoubleLinkAxis.ConvertTree ((Axis) (ast.Input)), false));
                    }
                    else {
                        this.fAxisArray.Add ( new ForwardAxis ( DoubleLinkAxis.ConvertTree (ast), false));
                    }
                    continue;
                }
                if (! IsDescendantOrSelf (stepAst)) {
                    throw new XmlSchemaException(Res.Sch_ICXpathError, xPath);
                }
                try {
                    stepAst = (Axis) (stepAst.Input);
                }
                catch {
                    throw new XmlSchemaException(Res.Sch_ICXpathError, xPath);
                }
                if ((stepAst == null) || (! IsSelf (stepAst)) || (stepAst.Input != null)) {
                    throw new XmlSchemaException(Res.Sch_ICXpathError, xPath);
                }

                // trim top "." if it's not the only node
                if (IsSelf(ast) && (ast.Input != null)) {
                    this.fAxisArray.Add ( new ForwardAxis ( DoubleLinkAxis.ConvertTree ((Axis) (ast.Input)), true));
                }
                else {
                    this.fAxisArray.Add ( new ForwardAxis ( DoubleLinkAxis.ConvertTree (ast), true));
                }
            }
        }