- "Traces FUNCTION with trace output going to BUFFER.
-For every call of FUNCTION Lisp-style trace messages that display argument
-and return values will be inserted into BUFFER. This function generates the
-trace advice for FUNCTION and activates it together with any other advice
-there might be!! The trace BUFFER will popup whenever FUNCTION is called.
-Do not use this to trace functions that switch buffers or do any other
-display oriented stuff, use `trace-function-background' instead.
-
-To untrace a function, use `untrace-function' or `untrace-all'."
+ "Trace calls to function FUNCTION.
+With a prefix argument, also prompt for the trace buffer (default
+`trace-buffer'), and a Lisp expression CONTEXT.
+
+Tracing a function causes every call to that function to insert
+into BUFFER Lisp-style trace messages that display the function's
+arguments and return values. It also evaluates CONTEXT, if that is
+non-nil, and inserts its value too. For example, you can use this
+to track the current buffer, or position of point.
+
+This function creates BUFFER if it does not exist. This buffer will
+popup whenever FUNCTION is called. Do not use this function to trace
+functions that switch buffers, or do any other display-oriented
+stuff - use `trace-function-background' instead.
+
+To stop tracing a function, use `untrace-function' or `untrace-all'."