${ThisOne}
${This${One}}
${This${One}Too}
${This${One}and${also}this}
...

##</code><code>##

m/
  \$\{(
    [^\{\$\}]*
    (?:
       \$\{
          [^\$\{\}]+
       \}
       [^\$\{\}]*
    )*
  )\}
/gxs;