how to write 'cross-staff slur'?

[compilelife]

musescore manual about this: https://musescore.org/zh-hans/%e7%94%a8%e6%88%b7%e6%89%8b%e5%86%8c/%e8%bf%9e%e5%8f%a5%e7%ba%bf

I'm wondering about how to write this in abc ?

or if abc2svg not support this, how may i improve abc2svg to support it? any advise? thanks