Vim copied and pasted content from other places. Why does tab appear after formatting?

  question, vim

Fig. 1, copy the code on a web page, paste it into vim editor, and pressgg=GAfter indenting, a vertical line appears at the front end of line 4, and looking at that distance, it istabThe spacing of the.
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Figure 2. Save the content and close it. Open vim again to edit this file. Pressgg=GIndent, the format is normal this time, the leftmost number on line 4 is four spaces.
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Why directly copy and paste the contentsgg=GWhat kind of situation will happen?

That’s not a vertical line, that’s vim’s screen is not redrawn, in normal mode,ctrl-lRedrawing the screen.