Tips in Allowed html tags

When you click on the "Allowed html-tags" pops up a window with valid tags, in which the paired tags are indicated, for example, <b> </ b>

But the tag <a href=''> for some reason did not receive this honor = (
At first it was thought that a mistake, but looking at everything else, I decided that it was such a feature, but it turned out that it was not = (