Makes the DocumentRange object uneditable.
Use the GetAsFrozen method to improve performance when it is necessary to retrieve information from many document ranges, i.e., syntax highlighting.
After this method is called, RichEditControl or RichEditDocumentServer stops tracking the actual document position for this range.
After the DocumentRange.GetAsFrozen method is executed, the target ranges cannot be modified. The frozen document ranges become invalid after the document is modified. Don't use these ranges for further document processing operations.