nl_tokens: http : // www . quirksmode . org / viewport / compatibility . html
pl_tokens: function jscoverage_getViewportHeight ( ) { //#JSCOVERAGE_IF /MSIE/.test(navigator.userAgent)
   if ( self . innerHeight ) { // all except Explorer
   return self . innerHeight ; } else if ( document . documentElement && document . documentElement . clientHeight ) { // Explorer 6 Strict Mode
   return document . documentElement . clientHeight ; } else if ( document . body ) { // other Explorers
   return document . <mask> . clientHeight ; } else { throw "Couldn't calculate viewport height" ; } //#JSCOVERAGE_ENDIF
   }