/aaaa $str... bbb/
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Groovy script
  Compound regular expression
    PsiElement(regex begin)('/')
    GrStringContentImpl(GString content element)
      PsiElement(regex content)('aaaa ')
    GString injection
      PsiElement($)('$')
      Reference expression
        PsiElement(identifier)('str')
    GrStringContentImpl(GString content element)
      PsiElement(regex content)('... bbb')
    PsiElement(regex end)('/')