Example
tightest
line
height
tight
line
height
natural
line
height
base
line
height
loose
line
height
looser
line
height
loosest
line
height
Markup
 <div class="grid-12 grid-parent">
  <div class="grid-1 text_lineHeightTightest">tightest<br/>line<br/>height</div>
  <div class="grid-1 text_lineHeightTight">tight<br/>line<br/>height</div>
  <div class="grid-2 text_lineHeightNatural">natural<br/>line<br/>height</div>
  <div class="grid-2 text_lineHeightBase">base<br/>line<br/>height</div>
  <div class="grid-2 text_lineHeightLoose">loose<br/>line<br/>height</div>
  <div class="grid-2 text_lineHeightLooser">looser<br/>line<br/>height</div>
  <div class="grid-2 text_lineHeightLoosest">loosest<br/>line<br/>height</div>
 </div>
Source: text/fonts.less, line 43