Indentation Width

If anyone is having the same struggle trying to change indentation width from 2 spaces to 4, try altering the variable `sgml-basic-offset`. I had previously altered `sgml-shift-width`, which was apparently sufficient for other modes, including `web-mode`, `react-mode`, `rjsx-mode`, and `js2-mode`, but not for this one.

Besides this, great experience so far.

Start by reproducing the indentation behavior in vue-mode and compare the roles of `sgml-basic-offset` and `sgml-shift-width`, including the other modes mentioned in the report. The issue does not identify a file, test, or specific desired change, so clarify the expected indentation configuration and define a regression check before implementation.

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