Fails to add prefix for class names using characters escaping (with backslash)

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In CSS, it is possible to escape characters to use them in class name. For example if you want a class name that starts with a digit, say "1st", it is totally valid to escape it, ending with a CSS selector .\31 st (notice the space inside a selector that only indicates the end of escaping sequence). Then you can use it normally, as <div class="1st" />. The same applies to SVG, and it happens for example when SVG files are being exported from Adobe Illustrator with "unique classnames" option.

The loader fails to add a prefix to selector in