mm.1: cat(1p) and tee(1p) provide similar functionality

docs/mm.1

@@ -26,7 +26,7 @@ Catenate input files and write them to the start of each output file or stream.
 
 .B -a
 .RS
-Opens outputs for appending rather than updating.
+Opens subsequent outputs for appending rather than updating.
 .RE
 
 .B -e
@@ -37,13 +37,16 @@ Use the standard error as an output.
 .B -i
 .RS
 Opens a path as an input. Without any inputs specified mm will use the
-standard input.
+standard input. The standard input shall be used as an input if one or more of
+the input files is “-”.
 .RE
 
 .B -o
 .RS
 Opens a path as an output. Without any outputs specified mm will use the
-standard output.
+standard output. The standard output shall be used as an output if one or more
+of the output files is “-”.
+
 .RE
 
 .B -u
@@ -56,11 +59,6 @@ Ensures neither input or output will be buffered.
 Causes SIGINT signals to be ignored.
 .RE
 
-.SH STANDARD INPUT
-
-The standard input shall be used as an input if one or more of the input files
-is “-”.
-
 .SH DIAGNOSTICS
 
 If an output can no longer be written mm prints a diagnostic message, ceases
@@ -76,9 +74,9 @@ Existing files are not truncated on ouput and are instead overwritten.
 
 .SH RATIONALE
 
-The cat(1p) and tee(1p) programs specified in POSIX together provide nearly
-equivalent functionality. The separation of the two sets of functionality into
-separate APIs seemed unncessary.
+The cat(1p) and tee(1p) programs specified in POSIX together provide similar
+functionality. The separation of the two sets of functionality into separate
+APIs seemed unncessary.
 
 .SH COPYRIGHT