nth-match is supposed to work in jsfiddle following way
:nth-match(even of p,h3) {text-decoration: underline;}
this should underline every
CSS4 selectors don't have much browser support at the moment, see here.
You could use nth-of-type, a CSS3 selector that has greater browser support (see here):
nth-of-type
p:nth-of-type(even) {text-decoration: underline;}
DEMO