--- a/runtime/doc/channel.txt
+++ b/runtime/doc/channel.txt
@@ -1,4 +1,4 @@
-*channel.txt*      For Vim version 7.4.  Last change: 2016 May 24
+*channel.txt*      For Vim version 7.4.  Last change: 2016 May 29
 
 
 		  VIM REFERENCE MANUAL	  by Bram Moolenaar
@@ -578,8 +578,8 @@ See |job_setoptions()| and |ch_setoption
 "exit_cb": handler	Callback for when the job ends.  The arguments are the
 			job and the exit status.
 			Vim checks about every 10 seconds for jobs that ended.
-			The callback can also be triggered by calling
-			|job_status()|.
+			The check also be triggered by calling |job_status()|,
+			which may then invoke the exit_cb handler.
 			Note that data can be buffered, callbacks may still be
 			called after the process ends.
 							*job-timeout*
@@ -625,18 +625,22 @@ See |job_setoptions()| and |ch_setoption
 "out_io": "null"	disconnect stdout (goes to /dev/null)
 "out_io": "pipe"	stdout is connected to the channel (default)
 "out_io": "file"	stdout writes to a file
-"out_io": "buffer" 	stdout appends to a buffer
+"out_io": "buffer" 	stdout appends to a buffer (see below)
 "out_name": "/path/file" the name of the file or buffer to write to
 "out_buf": number	the number of the buffer to write to
+"out_modifiable": 0	when writing to a buffer, 'modifiable' will be off
+			(see below)
 
 				*job-err_io* *err_name* *err_buf*
 "err_io": "out"		stderr messages to go to stdout
 "err_io": "null"	disconnect stderr  (goes to /dev/null)
 "err_io": "pipe"	stderr is connected to the channel (default)
 "err_io": "file"	stderr writes to a file
-"err_io": "buffer" 	stderr appends to a buffer
+"err_io": "buffer" 	stderr appends to a buffer (see below)
 "err_name": "/path/file" the name of the file or buffer to write to
 "err_buf": number	the number of the buffer to write to
+"err_modifiable": 0	when writing to a buffer, 'modifiable' will be off
+			(see below)
 
 "block_write": number	only for testing: pretend every other write to stdin
 			will block
@@ -663,6 +667,15 @@ used to get the buffer number.
 For a new buffer 'buftype' is set to "nofile" and 'bufhidden' to "hide".  If
 you prefer other settings, create the buffer first and pass the buffer number.
 
+The "out_modifiable" and "err_modifiable" options can be used to set the
+'modifiable' option off, or write to a buffer that has 'modifiable' off.  That
+means that lines will be appended to the buffer, but the user can't easily
+change the buffer.
+
+When an existing buffer is to be written where 'modifiable' is off and the
+"out_modifiable" or "err_modifiable" options is not zero, an error is given
+and the buffer will not be written to.
+
 When the buffer written to is displayed in a window and the cursor is in the
 first column of the last line, the cursor will be moved to the newly added
 line and the window is scrolled up to show the cursor if needed.