I'll try to explain with an example.
Sets the function
wpdt_list_categories (showselection = 1 & listposts = 0) as the 100 posts on the blog to display in the list makes no sense to then turn off
listposts = 0. To navigate
showselection = 1 connect to a visitor of the blog understand where and in what category it belongs. So if I go to the post as the list is minimized, and the visitor does not understand where and in what category it belongs. You can implement in your function, so that when a visitor goes to the post list is not folded, and remained open and the category assigned a class = "nodeSel" belongs to the post.