message: Simplify RE_COMMON_PLACEHOLDERS
  Use the \w shorthand for word characters group to make the regex shorter
  and more readable. Remove superfluous capture groups.
diff: @@ -209,8 +209,19 @@ std::wregex RE_PYTHON_FORMAT(LR"((%(\(\w+\))?[-+ #0]?(\d+|\*)?(\.(\d+|\*))?[hlL]
  std::wregex RE_RUBY_FORMAT(LR"(%(\d+\$)?[-+ #0]{0,5}(\d+|\*)?(\.(\d+|\*))?(hh|ll|[hljztL])?[%csdioxXufFeEaAgGnp])",
  std::regex_constants::ECMAScript | std::regex_constants::optimize);
  -// variables expansion for %foo% (Twig), %{foo} (Ruby), {foo} and {{foo}}
  -std::wregex RE_COMMON_PLACEHOLDERS(LR"((%[0-9a-zA-Z_.-]+%)|(%?\{[0-9a-zA-Z_.-]+\})|(\{\{[0-9a-zA-Z_.-]+\}\}))",
  +// variables expansion for various template languages
  +std::wregex RE_COMMON_PLACEHOLDERS(
  + //
  + // | |
  + LR"(%[\w.-]+%|%?\{[\w.-]+\}|\{\{[\w.-]+\}\})",
  + // | | | | |
  + // | | |
  + // | | +----------------------- {{var}}
  + // | |
  + // | +--------------------------------------- %{var} (Ruby) and {var}
  + // |
  + // +--------------------------------------------------- %var% (Twig)
  + //
  std::regex_constants::ECMAScript | std::regex_constants::optimize);
  } // anonymous namespace
  