Clarify current trailing comma behavior in the docs
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@ -244,16 +244,6 @@ required due to an inner function starting immediately after.
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_Black_ will add trailing commas to expressions that are split by comma where each
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element is on its own line. This includes function signatures.
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Unnecessary trailing commas are removed if an expression fits in one line. This makes it
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1% more likely that your line won't exceed the allotted line length limit. Moreover, in
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this scenario, if you added another argument to your call, you'd probably fit it in the
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same line anyway. That doesn't make diffs any larger.
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One exception to removing trailing commas is tuple expressions with just one element. In
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this case _Black_ won't touch the single trailing comma as this would unexpectedly
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change the underlying data type. Note that this is also the case when commas are used
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while indexing. This is a tuple in disguise: `numpy_array[3, ]`.
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One exception to adding trailing commas is function signatures containing `*`, `*args`,
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or `**kwargs`. In this case a trailing comma is only safe to use on Python 3.6. _Black_
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will detect if your file is already 3.6+ only and use trailing commas in this situation.
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@ -262,6 +252,10 @@ in function signatures that have stars in them. In other words, if you'd like a
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comma in this situation and _Black_ didn't recognize it was safe to do so, put it there
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manually and _Black_ will keep it.
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A pre-existing trailing comma informs _Black_ to always explode contents of the current
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bracket pair into one item per line. Read more about this in the
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[Pragmatism](#pragmatism) section below.
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### Strings
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_Black_ prefers double quotes (`"` and `"""`) over single quotes (`'` and `'''`). It
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