Custom regexp for mention

[deguif]

I don't see any possibility to handle custom mention regexp.
Would it be usefull to add support for it?

For example: in my use case, a username can be composed of several characters that are not allowed in regexp used for twitter or instagram (for example -, +, ...). They are not referencing twitter or instagram username.

This could introduce a new way to configure mention, using an object instead of only a string consisting of the service name. Here's an example:

mention: {
    regexp: '',
}

[CaitlinP95]

^^ this would be super useful. I've had to disable my hashtags from containing hyphens; twitter, facebook, and Instagram does not seem to support them. Has any progress been made with this?