[DOC] Describe `$F`

This variation is used when `-a` option is given.

1 files changed, 7 insertions, 0 deletions

diff --git a/doc/language/globals.md b/doc/language/globals.md
index 7030cc1bfd..b22363f1da 100644
--- a/doc/language/globals.md
+++ b/doc/language/globals.md
@@ -79,6 +79,7 @@ require 'English'
 |    `$-i`    |         | Extension given with command-line option `-i`. |
 |    `$-l`    |         | Whether option `-l` was given.                 |
 |    `$-p`    |         | Whether option `-p` was given.                 |
+|    `$F`     |         | Array of `$_` split by `$-F`.                  |
 
 ## Exceptions
 
@@ -378,6 +379,12 @@ Whether command-line option `-l` was set; read-only.
 
 Whether command-line option `-p` was given; read-only.
 
+### `$F`
+
+If the command line option `-a` is given, the array obtained by
+splitting `$_` by `$-F` is assigned at the start of each `-l`/`-p`
+loop.
+
 ## Deprecated
 
 ### `$=`