IMHO the simplest (and most generally useful) workaround is to put complex sub-patterns into variables and to use /x-option for readability:

  DB<101> $_=" x 3 "
 => " x 3 "
 
  DB<102> $s='[\s\xA0]'
 => "[\\s\\xA0]"
 
  DB<103> s/$s (x) $s/$1/x
 => 1
 
  DB<104> $_
 => "x3 "
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