Clear is a procedure used to remove all existing data in the internal storage for the buffer. Clear sets the length of the internal storage for the buffer to 0 (zero). 

Clear is called from both the constructor and destructor for the object instance. 

Use Remove to discard a specified number of bytes in the internal storage for the buffer. 

Use Extract to retrieve data from the buffer for subsequent use prior to removal from the internal storage.

TIdBuffer.Extract 

TIdBuffer.Remove 

TIdBuffer.Create 

TIdBuffer.Destroy