Something similar opportunity is DEFINE.

Example:
    (?(DEFINE)(?<myname>\bvery\b))(?&myname)\p{Pd}(?&myname).

Expression above will match "very-very" from next sentence:
    Define is very-very handy sometimes.
              ^-------^

How it works. (?(DEFINE)(?<myname>\bvery\b)) - this block defines "myname" equal to "\bvery\b". So, this block "(?&myname)\p{Pd}(?&myname)" equvivalent to "\bvery\b\p{Pd}\bvery\b".

The escape sequence \g used as a backreference may not always behave as expected.
The following numbered backreferences refer to the text matching the specified capture group, as documented:
\1
\g1
\g{1}
\g-1
\g{-1}

However, the following variants refer to the subpattern code instead of the matched text:
\g<1>
\g'1'
\g<-1>
\g'-1'

With named backreferences, we may also use the \k escape sequence as well as the (?P=...) construct. The following combinations also refer to the text matching the named capture group, as documented:
\g{name}
\k{name}
\k<name>
\k'name'
(?P=name)

However, these refer to the subpattern code instead of the matched text:
g<name>
\g'name'

In the following example, the capture group searches for a single letter 'a' or 'b', and then the backreference looks for the same letter. Thus, the patterns are expected to match 'aa' and 'bb', but not 'ab' nor 'ba'.

<?php
/* Matches to the following patterns are replaced by 'xx' in the subject string 'aa ab ba bb'. */
$patterns = [
  # numbered backreferences (absolute)
  '/([ab])\1/',      // 'xx ab ba xx'
  '/([ab])\g1/',     // 'xx ab ba xx'
  '/([ab])\g{1}/',   // 'xx ab ba xx'
  '/([ab])\g<1>/',   // 'xx xx xx xx' # unexpected behavior, backreference matches both 'a' and 'b'.
  "/([ab])\g'1'/",   // 'xx xx xx xx' # unexpected behavior, backreference matches both 'a' and 'b'.
  '/([ab])\k{1}/',   // 'aa ab ba bb' # No group with name "1", backreference to unset group always fails.
  '/([ab])\k<1>/',   // 'aa ab ba bb' # No group with name "1", backreference to unset group always fails.
  "/([ab])\k'1'/",   // 'aa ab ba bb' # No group with name "1", backreference to unset group always fails.
  '/([ab])(?P=1)/',  // NULL # Regex error: "subpattern name must start with a non-digit", (?P=) expects name not number.
  # numbered backreferences (relative)
  '/([ab])\-1/',     // 'aa ab ba bb'
  '/([ab])\g-1/',    // 'xx ab ba xx'
  '/([ab])\g{-1}/',  // 'xx ab ba xx'
  '/([ab])\g<-1>/',  // 'xx xx xx xx' # unexpected behavior, backreference matches both 'a' and 'b'.
  "/([ab])\g'-1'/",  // 'xx xx xx xx' # unexpected behavior, backreference matches both 'a' and 'b'.
  '/([ab])\k{-1}/',  // 'aa ab ba bb' # No group with name "-1", backreference to unset group always fails.
  '/([ab])\k<-1>/',  // 'aa ab ba bb' # No group with name "-1", backreference to unset group always fails.
  "/([ab])\k'-1'/",  // 'aa ab ba bb' # No group with name "-1", backreference to unset group always fails.
  '/([ab])(?P=-1)/', // NULL # Regex error: "subpattern name expected", (?P=) expects name not number.
  # named backreferences
  '/(?<name>[ab])\g{name}/',  // 'xx ab ba xx'
  '/(?<name>[ab])\g<name>/',  // 'xx xx xx xx' # unexpected behavior, backreference matches both 'a' and 'b'.
  "/(?<name>[ab])\g'name'/",  // 'xx xx xx xx' # unexpected behavior, backreference matches both 'a' and 'b'.
  '/(?<name>[ab])\k{name}/',  // 'xx ab ba xx'
  '/(?<name>[ab])\k<name>/',  // 'xx ab ba xx'
  "/(?<name>[ab])\k'name'/",  // 'xx ab ba xx'
  '/(?<name>[ab])(?P=name)/', // 'xx ab ba xx'
];
    
foreach ($patterns as $pat)
    echo "  '$pat',\t// " . var_export(@preg_replace($pat, 'xx', 'aa ab ba bb'), 1) . PHP_EOL;
?>