Should we have a better \index macro?

[kbeyls]

When writing, it's easy to forget that the text in an \index{} entry is not also put in the main text.

For example,
The content of the \index{cache} is...
will render as
The content of the is.

Maybe we could construct a better macro where the content between the curly braces is also present in the main text?
Probably one of the hard parts to implement that is that the \index{} macro is only processed when LaTeX/PDF is produced, not when the HTML version of the book is produced.
We'd have to find a mechanism that works for both PDF and HTML production.

At the moment, we do not have an index in the HTML version of the book. Implementing the above idea might also help in making sure we have an index in the HTML version of the book?