/* spec information about this property
name= letter-spacing
css1= http://www.w3.org/TR/2008/REC-CSS1-20080411/#letter-spacing
css2= http://www.w3.org/TR/2008/REC-CSS2-20080411/text.html#propdef-letter-spacing
css21= http://www.w3.org/TR/2011/REC-CSS2-20110607/text.html#propdef-letter-spacing 
css3= https://www.w3.org/TR/2017/WD-css-text-3-20170822/#letter-spacing-property
*/