+It currently does I<not> mimic MS-DOS as far as treating of Control-Z
+as being an end-of-file marker.
+
+(Gory details follow) To be more exact what happens is this: after
+pushing itself to the stack, the C<:crlf> layer checks all the layers
+below itself to find the first layer that is capable of being a CRLF
+layer but is not yet enabled to be a CRLF layer. If it finds such a
+layer, it enables the CRLFness of that other deeper layer, and then
+pops itself off the stack. If not, fine, use the one we just pushed.
+
+The end result is that a C<:crlf> means "please enable the first CRLF
+layer you can find, and if you can't find one, here would be a good
+spot to place a new one."
+
+Based on the C<:perlio> layer.
+
+=item :mmap
+
+A layer which implements "reading" of files by using C<mmap()> to
+make (whole) file appear in the process's address space, and then
+using that as PerlIO's "buffer". This I<may> be faster in certain
+circumstances for large files, and may result in less physical memory
+use when multiple processes are reading the same file.
+
+Files which are not C<mmap()>-able revert to behaving like the C<:perlio>
+layer. Writes also behave like C<:perlio> layer as C<mmap()> for write
+needs extra house-keeping (to extend the file) which negates any advantage.
+
+The C<:mmap> layer will not exist if platform does not support C<mmap()>.
+
+=item :utf8
+
+Declares that the stream accepts perl's I<internal> encoding of