(Time of Day): Document float-time.

(Recording Input): Document that clear-this-command-keys clears
the vector returned by recent-keys.

lispref/os.texi

@@ -995,6 +995,18 @@ integers.  Thus, you can use times obtained from @code{current-time}
 (see above) and from @code{file-attributes} (@pxref{File Attributes}).
 @end defun
 
+@defun float-time &optional time-value
+This function returns the current time as a floating-point number of
+seconds since the epoch.  The argument @var{time-value}, if given,
+specifies a time to convert instead of the current time.  The argument
+should have the same form as for @code{current-time-string} (see
+above), and it also accepts the output of @code{current-time} and
+@code{file-attributes}.
+
+@emph{Warning}: Since the result is floating point, it may not be
+exact.  Do not use this function if precise time stamps are required.
+@end defun
+
 @node Time Conversion
 @section Time Conversion
 
@@ -1619,6 +1631,9 @@ they were used as parts of key sequences.  Thus, you always get the last
 100 input events, not counting events generated by keyboard macros.
 (These are excluded because they are less interesting for debugging; it
 should be enough to see the events that invoked the macros.)
+
+A call to @code{clear-this-command-keys} (@pxref{Command Loop Info})
+causes this function to return an empty vector.
 @end defun
 
 @deffn Command open-dribble-file filename