That people produce HTML with string templates is telling us something
A while back I had a hot take on the Fediverse:
Another day, another 'producing HTML with string templates/interpolation is wrong' article. People have been writing these articles for a decade or more and people doing web development have kept voting with their feet, which is why we have string templates everywhere. At this point, maybe people should consider writing about why things have worked out this way.
(I don't think it's going to change, either. No one has structured HTML creation that's as easy as string templates.)
One of my fundamental rules of system design is when people keep doing it wrong, the people are right and your system or idea is wrong. A corollary to this is that when you notice this happening, a productive reaction is to start asking questions about why people do it the 'wrong' way. Despite what you might expect from its title, Hugo Landau's [[Producing HTML using string templates has always been the wrong solution (via) actually has some ideas and pointers to ideas, for instance this quote from Using type inference to make web templates robust against XSS:
Strict structural containment is a sound, principled approach to building safe templates that is a great approach for anyone planning a new template language, but it cannot be bolted onto existing languages though because it requires that every element and attribute start and end in the same template. This assumption is violated by several very common idioms, such as the header-footer idiom in ways that often require drastic changes to repair.
Another thing to note here is that pretty much every programming language has a way to format strings, and many of them have ways to have multi-line strings. This makes producing HTML via string formatting something that scales up (and down) very easily; you can use the same idiom to format a small snippet as you would a large block. Even Go's html/template package doesn't scale down quite that far, although it comes close. String templating is often very close to string formatting and so probably fits naturally into how programmers are acclimatized to approach things.
(Hugo Landau classifies Go's html/template as 'context aware autoescaping HTML string templating', and considers it not as good as what the quote above calls 'strict structural containment' that works on the full syntax tree of the HTML document.)
I don't have any particular answers to why string templating has been enduringly popular so far (although I can come up with theories, including that string templating is naturally reusable to other contexts, such as plain text). But that it has suggests that people see string templating as having real advantages over their alternatives and those advantages keep being compelling, including in new languages such as Go (where the Go authors created html/template instead of trying to define a 'strict structural containment' system). If people want to displace string templating, figuring out what those current advantages are and how to duplicate them in alternatives seems likely to be important.
(I'll pass on the question of how important it is to replace the most powerful context aware autoescaping HTML string templating with something else.)
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