The following patch adds a short description of the os.sleep() function 
which is undocumented to the manual. The C source code of the os.sleep()
function can be found here:
https://gitlab.lisn.upsaclay.fr/texlive/luatex/-/blob/master/source/texk/web2c/luatexdir/lua/loslibext.c#L663-673

In addition, the patch documents the optional argument template of the os.tmpdir([template]) function:
https://gitlab.lisn.upsaclay.fr/texlive/luatex/-/blob/master/source/texk/web2c/luatexdir/lua/loslibext.c#L971-997

The patch also fixes a few whitespace issues.

See attached patch file.

diff --git a/manual/luatex-lua.tex b/manual/luatex-lua.tex
index 94dead9e1..01b39d832 100644
--- a/manual/luatex-lua.tex
+++ b/manual/luatex-lua.tex
@@ -434,8 +434,9 @@ used as building blocks for other helpers.

 The \type {os} library has a few extra functions and variables: \libidx {os}
 {selfdir}, \libidx {os} {exec}, \libidx {os} {spawn}, \libidx {os} {setenv},
-\libidx {os} {env}, \libidx {os} {gettimeofday}, \libidx {os} {times}, \libidx
-{os} {tmpdir}, \libidx {os} {type}, \libidx {os} {name} and \libidx {os} {uname},
+\libidx {os} {env}, \libidx {os} {gettimeofday}, \libidx {os} {times},
+\libidx {os} {sleep}, \libidx {os} {tmpdir}, \libidx {os} {type},
+\libidx {os} {name} and \libidx {os} {uname},
 that we will discuss here.

 \startitemize
@@ -522,19 +523,29 @@ that we will discuss here.
 \stopitem

 \startitem
-    \type {os.times()}returns the current process times according to \ the
+    \type {os.times()} returns the current process times according to the
     \UNIX\ C library function \quote {times}. This function is not available on
     the \MSWINDOWS\ and \SUNOS\ platforms, so do not use this function for
     portable documents.
 \stopitem

 \startitem
-    \type {os.tmpdir()} creates a directory in the \quote {current directory}
+    \type {os.sleep(interval[, unit])} suspends the execution of the current run for
+    a given number of seconds. If the optional argument \type {unit} is present, the
+    function waits \type {interval / units} seconds. \type {os.sleep(1, 1000)}
+    for example pauses the program for one millisecond.
+\stopitem
+
+\startitem
+    \type {os.tmpdir([template])} creates a directory in the \quote {current directory}
     with the name \type {luatex.XXXXXX} where the \type {X}-es are replaced by a
     unique string. The function also returns this string, so you can \type
     {lfs.chdir()} into it, or \type {nil} if it failed to create the directory.
     The user is responsible for cleaning up at the end of the run, it does not
-    happen automatically.
+    happen automatically. You can also use your own \type {template} for the name
+    of the temporary folder. However, the passed string must end with six capital
+    \type {X}-es. For example, the template \type {tmp.XXXXXX} could result in the
+    folder name \type {tmp.vX3gPo}.
 \stopitem

 \startitem