I've given some thought to this kind of string literal in the past (for my imaginary programming language). I want a syntax something like this:

  var xml = """<element attr="content">
            """    <body>
            """    </body>
            """</element>
            """;

This would give you the string:

  <element attr="content">
      <body>
      </body>
  </element>(no newline)

If you wanted a newline at the end, you'd do this:

  var xml = """<element attr="content">
            """    <body>
            """    </body>
            """</element>
            """
            """;

Basically the end delimiter of the string would be the last """. You could concatenate two strings like so:

  var xml = """<element attr="content">
            """    <body>
            """    </body>
            """</element>
            """
            """ // this string ended on this line
            + 
            """<element attr="content">
            """    <body>
            """    </body>
            """</element>
            """
            """; // this string ended on this line

This could use the same logic for using at least three quotes as the indicator that it's a multiline string.

Please, tear this apart and offer improvements.

Edit: this is conceptually similar to Zig's multiline literal: https://ziglang.org/documentation/master/#Multiline-String-L...