Mixed spaces and tabs in indentions

Here's a situation the results in a mix of tabs and spaces in an indent - disastrous.

There's source code somewhere outside the editor (maybe web page, maybe a text editor) that includes a tab followed by spaces within an indent of a line. Copying and pasting that code into the online editor doesn't result in the space being converted; in fact, it seems an even stranger mix of spaces and tabs results in that line's indent. Although the code still _appears_ fine on screen (in online editor), it won't work properly on the micro:bit.

No file, test, or entry point is named. Start by reproducing the issue in the online editor with pasted code containing a tab followed by spaces in an indent, then compare the resulting indentation with the code run on the micro:bit. Done should mean this input no longer produces invalid indentation, but the intended normalization behavior is not specified.

Written by the indexing model from the issue text.