Thank you for your very useful feedback :)

A native representation of HTML tags is a good idea: I'll have to do that.

For ...---, I wanted a big split symbol between branches (||========) and a small split symbol between the two steps inside a branch (...---). ... because the branch continues and --- to mark a smaller split than ==========.

I intend to add a syntaxic sugar for:

parallel(select N) ||
||==============
    myFunction(arg1,...,argM)
...--------
    restOfBranch1
||=============
    myFunction(arg1b,...,argMb)
...-------
    restOfBranch2

that would be:

choose N by myFunction
    * arg1,...,argM
        restOfBranch1
    * arg1b,...,argMb
        restOfBranch2