TAppendFileStream = class(TIdFileStream);

TAppendFileStream is a TIdFileStream descendant that implements a file stream used to append content to a file in the local file system. 

TAppendFileStream implements a constructor that accepts a file name representing the storage for the file stream. 

The constructor ensures that the underlying file stream is opened or created using the correct file mode and sharing mode for the specified file name. The constructor also positions the stream at its end when the file already exists. 

Use TFileCreateStream when a file stream is required that always recreates the underlying file storage for the stream. 

Use TReadFileExclusiveStream or TReadFileNonExclusiveStream to create file streams with the desired file sharing modes enabled.