Multiple shell parameter assignments prefixing a bash command - bash

Question

In the bash manual section 3.7.4, it states
The environment for any simple command or function may be augmented
temporarily by prefixing it with parameter assignments, as described
in Shell Parameters [section 3.4].
And a trivial example of this is
MYVAR=MYVALUE mycommand
I have read section 3.4 and I still can't figure out how to specify multiple parameter assignments. Note that the statement in 3.7.4 is definitely plural, implying that it is possible.
The following does not seem to work:
MYVAR1=abc MYVAR2=xyz mycommand
I am using bash version 4.1, 23 December 2009.

Answer 1

It should work. That is acceptable syntax. Here's an example:
$ cat a
#!/bin/sh
echo $MYVAR1
echo $MYVAR2
$ ./a
$ MYVAR1=abc MYVAR2=xyz ./a
abc
xyz
$
UPDATE: Your updated example given in your answer will work if you precede the simple command with the variables as required:
mycommand () { echo MYVAR1=[$MYVAR1]; echo MYVAR2=[$MYVAR2]; }
for f in ~/*.txt ; do MYVAR1=abc MYVAR2=xyz mycommand; done

Answer 2

Oops, my example was over-simplified. This works fine:
mycommand () { echo MYVAR1=[$MYVAR1]; echo MYVAR2=[$MYVAR2]; }
MYVAR1=abc MYVAR2=xyz mycommand
but this does not:
mycommand () { echo MYVAR1=[$MYVAR1]; echo MYVAR2=[$MYVAR2]; }
MYVAR1=abc MYVAR2=xyz for f in ~/*.txt; do mycommand; done
and the key difference is this phrase:
for any simple command or function
A for command is a complex command, not "a simple command or function", according to section 3.2.

Answer 3

I've never seen that method used.
You could always just pass in regular parameters to the script.
Updating for new example:
This works in both situations:
> mycommand () { echo MYVAR1=[$1]; echo MYVAR2=[$2]; }
> mycommand a b
MYVAR1=[a]
MYVAR2=[b]
> for f in ~/file*.txt; do mycommand a b; done
MYVAR1=[a]
MYVAR2=[b]
MYVAR1=[a]
MYVAR2=[b]