vim surrounding

在研究surrounding.vim时发现text object selection.

This is a series of commands that can only be used while in Visual mode or
after an operator.

• The commands that start with "a" select "a"n object
  including white space
•  the commands starting with "i" select an "inner" object
  without white space, or just the white space.
• a[w|W]
• i [w|W]
• as
• is
• at : a tag block. 比如有个html tag <a href="#">show</a> vat 会选中整个tag,including </a>
• it  : inner tag block ,only show will be selected.