[DOC] Mention "-" in ARGF

doc/globals.rdoc

@@ -269,6 +269,8 @@ Whether command-line option <tt>-a</tt> was given; read-only.
 Contains the extension given with command-line option <tt>-i</tt>,
 or +nil+ if none.
 
+An alias of ARGF.inplace_mode.
+
 ==== <tt>$-l</tt>
 
 Whether command-line option <tt>-l</tt> was set; read-only.
@@ -307,7 +309,7 @@ The standard error stream (the default value for <tt>$stderr</tt>):
 
 === Enviroment
 
-==== <tt>ENV</tt>
+==== ENV
 
 A hash of the contains current environment variables names and values:
 
@@ -319,10 +321,11 @@ A hash of the contains current environment variables names and values:
    ["DISPLAY", ":0"],
    ["GDMSESSION", "ubuntu"]]
 
-==== <tt>ARGF</tt>
+==== ARGF
 
-The virtual concatenation of the files given on the command line,
-or from <tt>$stdin</tt> if no files were given.
+The virtual concatenation of the files given on the command line, or from
+<tt>$stdin</tt> if no files were given, <tt>"-"</tt> is given, or after
+all files have been read.
 
 ==== <tt>ARGV</tt>
 

io.c

@@ -14625,11 +14625,16 @@ set_LAST_READ_LINE(VALUE val, ID _x, VALUE *_y)
  *     ARGV.replace ["file2", "file3"]
  *     ARGF.read      # Returns the contents of file2 and file3
  *
- * If +ARGV+ is empty, ARGF acts as if it contained STDIN, i.e. the data
- * piped to your script. For example:
+ * If +ARGV+ is empty, ARGF acts as if it contained <tt>"-"</tt> that
+ * makes ARGF read from STDIN, i.e. the data piped or typed to your
+ * script. For example:
  *
  *     $ echo "glark" | ruby -e 'p ARGF.read'
  *     "glark\n"
+ *
+ *     $ echo Glark > file1
+ *     $ echo "glark" | ruby -e 'p ARGF.read' -- - file1
+ *     "glark\nGlark\n"
  */
 
 /*