#one# -> <element name="one">
#two# -> <element name="two">

replaceAll("#[w]#", "<element name="[?1]"");
// my hope is that I can remember a value somehow (`[w]`) and use it for the substitution ([?1])
// which is, written like this, a nonsense

str = str.replaceAll("#(\w+)#", "<element name="$1">");