this 1000 means the priority.

 by how a priority can get 1000 ? for example what that mean a priority = 50 or 20 or 100 ?

http://reference.elgg.org/master/views_8php.html#a0e5a8f8b013ca895d006af29897c83fa

:-)

Use lower numbers to prepend your view or higher numbers to append your view. The number you use doesn't matter unless you're using priority in menus where the order matters. I usually use 0 to prepend my views. Example would be the top bar menus.

All view extensions are sorted using priority before display. The main view has the priority of 500. Generally it's recommended to use priorities from range 0 to 1000 and I'd say that using 0 or 1000 shouldn't be done to often by plugin devs as it defeats the purpose of having whole range of priorities.