System.Xml.Xsl.Runtime.DescendantMergeIterator.MoveNext C# (CSharp) Method

        public IteratorResult MoveNext(XPathNavigator input) {
            if (this.state != IteratorState.NeedDescendant) {
                if (input == null)
                    return IteratorResult.NoMoreNodes;

                // Descendants of the input node will be duplicates if the input node is in the subtree
                // of the previous root.
                if (this.state != IteratorState.NoPrevious && this.navRoot.IsDescendant(input))
                    return IteratorResult.NeedInputNode;

                // Save input node as current node and end of input's tree in navEnd
                this.navCurrent = XmlQueryRuntime.SyncToNavigator(this.navCurrent, input);
                this.navRoot = XmlQueryRuntime.SyncToNavigator(this.navRoot, input);
                this.navEnd = XmlQueryRuntime.SyncToNavigator(this.navEnd, input);
                this.navEnd.MoveToNonDescendant();

                this.state = IteratorState.NeedDescendant;

                // If self node matches, then return it
                if (this.orSelf && !this.filter.IsFiltered(input))
                    return IteratorResult.HaveCurrentNode;
            }

            if (this.filter.MoveToFollowing(this.navCurrent, this.navEnd))
                return IteratorResult.HaveCurrentNode;

            // No more descendants, so transition to NeedCurrent state and get the next input node
            this.state = IteratorState.NeedCurrent;
            return IteratorResult.NeedInputNode;
        }