Hi!
I have trouble to define macros which are only visible inside a block defined using `\definestartstop`:
```tex
\setuppapersize[A6]
\definestartstop[Foo][before={Foo}]
\definestartstop[Bar][before={\bgroup\define\Foo{Foo}},after={\egroup}]
%\definestartstop[Baz][before={\bgroup\define[1]\Foo{Foo#1}},after={\egroup}]
\starttext
\startFoo
Bar
\stopFoo
\startBar
\Foo Bar
\stopBar
% \startBaz
% \Foo{Bar}
% \stopBaz
\stoptext
```
The code as above works and typesets "FooBar" on two separate lines. But if I uncomment everything `Baz`-related, I end up with the following error:
```plain
tex error > error on line 4 in file C:/HIDDEN/mwe.tex: ! Illegal
parameter number in definition of \m_syst_action_yes
<to be read again>
1
<argument> ...{Baz}][{before={\bgroup \define [1]\Foo {Foo##1
}},after={\egroup }}]
\doifnextoptionalelse ...ef \m_syst_action_yes {#1
}\def \m_syst_action_nop {...
l.4 ...bgroup\define[1]\Foo{Foo#1}},after={\egroup}]
1 \setuppapersize[A6]
2 \definestartstop[Foo][before={Foo}]
3 \definestartstop[Bar][before={\bgroup\define\Foo{Foo}},after={\egroup}]
4 >> \definestartstop[Baz][before={\bgroup\define[1]\Foo{Foo#1}},after={\egroup}]
5
6 \starttext
7 \startFoo
8 Bar
9 \stopFoo
10
11 \startBar
12 \Foo Bar
13 \stopBar
14
```
Can someone help me get this running?