I would make your example a little safer:

my %data = $_ =~ m{
  ([^=\s]+) \s* = \s* 
  ["']? (
    (?<= '  ) [^']* (?=  '   ) |
    (?<=  " ) [^"]* (?=   "  ) |
    (?<!['"]) \S+   (?! ['"] )
  )["']?
}xg;
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That, to me, seems safer, because it ensures a string that starts quoted ends quoted, and a string that doesn't start quoted doesn't end quoted (for some bizarre reason).