[FOLD] add comments

Author: sdkrystian

clang/include/clang/Lex/Preprocessor.h

@@ -1160,6 +1160,8 @@ class Preprocessor {
   /// invoked (at which point the last position is popped).
   std::vector<CachedTokensTy::size_type> BacktrackPositions;
 
+  /// Stack of cached tokens/initial number of cached tokens pairs, allowing
+  /// nested unannotated backtracks.
   std::vector<std::pair<CachedTokensTy, CachedTokensTy::size_type>>
       UnannotatedBacktrackTokens;
 
@@ -1725,6 +1727,8 @@ class Preprocessor {
   /// at some point after EnableBacktrackAtThisPos. If you don't, caching of
   /// tokens will continue indefinitely.
   ///
+  /// \param Unannotated Whether token annotations are reverted upon calling
+  /// Backtrack().
   void EnableBacktrackAtThisPos(bool Unannotated = false);
 
 private:
@@ -1744,6 +1748,8 @@ class Preprocessor {
   /// caching of tokens is on.
   bool isBacktrackEnabled() const { return !BacktrackPositions.empty(); }
 
+  /// True if EnableBacktrackAtThisPos() was called and
+  /// caching of unannotated tokens is on.
   bool isUnannotatedBacktrackEnabled() const {
     return !UnannotatedBacktrackTokens.empty();
   }

clang/include/clang/Parse/Parser.h

@@ -1025,6 +1025,8 @@ class Parser : public CodeCompletionHandler {
   ///   ....
   ///   TPA.Revert();
   ///
+  /// If the Unannotated parameter is true, any token annotations created
+  /// during the tentative parse are reverted.
   class TentativeParsingAction {
     Parser &P;
     PreferredTypeBuilder PrevPreferredType;