LayoutConstrainsVisualFormat.txt

H: (Horizontal) //horizontal direction
V: (Vertical) //vertical direction
| (pipe) //superview
- (dash) //standard spacing (generally 8 points)
[] (brackets) //name of the object (uilabel, unbutton, uiview, etc.)
() (parentheses) //size of the object
== equal widths //can be omitted
-16- non standard spacing (16 points)
<= less than or equal to
>= greater than or equal to
@250 priority of the constraint //can have any value between 0 and 1000