diff --git a/DOCS/man/mpv.rst b/DOCS/man/mpv.rst
index e40acdcff1..aa68bee896 100644
--- a/DOCS/man/mpv.rst
+++ b/DOCS/man/mpv.rst
@@ -241,6 +241,16 @@ button 5 and button 6
 USAGE
 =====
 
+Command line arguments starting with ``-`` are interpreted as options,
+everything else as filenames or URLs. All options except *flag* options (or
+choice options which include ``yes``) require a parameter in the form
+``--option=value``.
+
+One exception is the lone ``-`` (without anything else), which means media data
+will be read from stdin. Also, ``--`` (without anything else) will make the
+player interpret all following arguments as filenames, even if they start with
+``-``. (To play a file named ``-``, you need to use ``./-``.)
+
 Every *flag* option has a *no-flag* counterpart, e.g. the opposite of the
 ``--fs`` option is ``--no-fs``. ``--fs=yes`` is same as ``--fs``, ``--fs=no``
 is the same as ``--no-fs``.
@@ -248,6 +258,24 @@ is the same as ``--no-fs``.
 If an option is marked as *(XXX only)*, it will only work in combination with
 the *XXX* option or if *XXX* is compiled in.
 
+Legacy option syntax
+--------------------
+
+The ``--option=value`` syntax is not strictly enforced, and the alternative
+legacy syntax ``-option value`` and ``--option value`` will also work. This is
+mostly  for compatibility with MPlayer. Using these should be avoided. Their
+semantics can change any time in the future.
+
+For example, the alternative syntax will consider an argument following the
+option a filename. ``mpv -fs no`` will attempt to play a file named ``no``,
+because ``--fs`` is a flag option that requires no parameter. If an option
+changes and its parameter becomes optional, then a command line using the
+alternative syntax will break.
+
+Currently, the parser makes no difference whether an option starts with ``--``
+or a single ``-``. This might also change in the future, and ``--option value``
+might always interpret ``value`` as filename in order to reduce ambiguities.
+
 Escaping spaces and other special characters
 --------------------------------------------