`str.format()` can only use substitutions identified by braces (`{` and
`}`). This has the potential to conflict with other code in the HTML
template, such as CSS or JavaScript.
Template strings can use substitutions identified by `$` or `${}`, e.g.:
`$identifier` or `${identifier}`. These substitutions won't conflict
with CSS or JavaScript, allowing users to write HTML templates that
don't require double braces anywhere there's a substitution conflict.
This is especially useful when one is using a build tool to generate the
final CSS/JavaScript/HTML.
https://docs.python.org/3/library/string.html#template-strings
