Position classes follow the following syntax:

size - direction - [media-query]

size - Seven options definied in variables: xxl, xl, lg, md, sm, xs, xxs or no for none
direction - Direction the position value is for: t, r, b, l
media-query - Breakpoint below which the class is active: lg, md, sm, xs (optional)

In addtion there are three classes for setting an elements position type

.pos-relative - [media-query]
.pos-absolute - [media-query]
.pos-fixed - [media-query]