Return callback for pre walk

[krzysztof-grzybek]

Related to #36

[coveralls]

Coverage increased (+0.09%) to 98.889% when pulling f36d330 on krzysztof-grzybek:return-callback-for-pre-walk into 1ac126a on joaonuno:master.

[joaonuno]

Hi, thank you for contributing! A few questions:

1. Can you give an example on the use-cases for this feature?
2. Is it only useful in depth-first pre-order strategy?
3. How is this related to issue 22?

[krzysztof-grzybek]

Hi Joanuno,
thank You for quick response.

1. I can describe my case which I'm struggling with:

I have layout data represented in Tree. I walk down the Tree and I add elements positioned absolute to the DOM. I keep top position in global variable. If node is group type, I insert child nodes inside (here top does not change). But after inserting all child nodes into the group, I have to increase my top value to render next sibling element below the group. The only thing comes to my mind is to increase it on hook after all child nodes has been visited.

If my explantion isn't clear let me know, I'll try to do it better :)

2. To be honest I didn't think about it, but probably it can be useful for all strategies.
3. Of course I linked wrong issue, sorry for that, it should issue Return callback for pre walk #36