When to add spaces after an inserted mention?

[artcodespace]

The current implementation of mentions as nodes adds a space only when there is no next sibling. This could be improved, for example if you have a mention directly next to am inline formatting node containing text, so you could end up with <mention /><strong>text</strong> and no space between the mention and the text.

Perhaps a better approach would start from:

Perhaps it's easier to define when we don't add a space. To me it seems that we shouldn't add a space if there is a leaf following the mention we've just added and that leaf doesn't already starts with a space. In all other cases add a space.

Testing for all the permutations of using a mention before other nodes would help smooth out the desired behaviour in all cases.