diff --git a/runtime/doc/builtin.txt b/runtime/doc/builtin.txt
index 1de0e40..12d62a6 100644
--- a/runtime/doc/builtin.txt
+++ b/runtime/doc/builtin.txt
@@ -6239,8 +6239,26 @@
 mkdir({name} [, {path} [, {prot}]])
 		Create directory {name}.
 
-		If {path} is "p" then intermediate directories are created as
-		necessary.  Otherwise it must be "".
+		If {path} contains "p" then intermediate directories are
+		created as necessary.  Otherwise it must be "".
+
+		If {path} contains "D" then {name} is deleted at the end of
+		the current function, as with: >
+			defer delete({name}, 'd')
+<
+		If {path} contains "R" then {name} is deleted recursively at
+		the end of the current function, as with: >
+			defer delete({name}, 'rf')
+<		Note that when {name} has more than one part and "p" is used
+		some directories may already exist.  Only the first one that
+		is created and what it contains is scheduled to be deleted.
+		E.g. when using: >
+			call mkdir('subdir/tmp/autoload', 'pR')
+<		and "subdir" already exists then "subdir/tmp" will be
+		scheduled for deletion, like with: >
+			defer delete('subdir/tmp', 'rf')
+<		Note that if scheduling the defer fails the directory is not
+		deleted.  This should only happen when out of memory.
 
 		If {prot} is given it is used to set the protection bits of
 		the new directory.  The default is 0o755 (rwxr-xr-x: r/w for