Confused about Twitter

Why do people type a period (a '.') before @ing another account?

>>1
if you do something like this:

@someone ur gay and most people won't see this

it won't show up for everyone, it's just a "mention" of that person
if you want to make that same tweet seen by all your followers, you start with regular text, THEN @ them, like so:

.@someone ur gay and I want all my followers to see this

this, along with "quote tweeting" are often used for harassment