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.

未指定檔案、測試或進入點。首先，在線上編輯器中貼上包含縮排中定位字元後接空格的程式碼來重現問題，然後將產生的縮排與在 micro:bit 上執行的程式碼進行比較。完成的標準應是此輸入不再產生無效縮排，但預期的正規化行為尚未指定。

由索引模型根據 Issue 內容生成。