Smart identation for `TextEdit`

I want to insert a extra line in textDocument/completion requests by additionalTextEdits.
However since I don't know the identation in this requests, I cannot choose the correct identation in TextEdit.
I know I can analyze context to guess the identation, but I hope this can be done by the client because the client knows the most correct indentation.

Currenty, if I set InsertTextFormat to Snippet, the \t in insertText can be smartly replaced to correct indentation.
So I hope TextEdit can support similar feature, for example:

interface TextEdit {
	/**
	 * The range of the text document to be manipulated. To insert
	 * text into a document create a range where start === end.
	 */
	range: Range;

	/**
	 * The string to be inserted. For delete operations use an
	 * empty string.
	 */
	newText: string;

	/**
	 * + 1: as is
	 * + 2: replace `\t` with correct indentation
	 */
	textFormat?: 1 | 2;
}

Start with the TextEdit and InsertTextFormat definitions in the LSP specification and compare them with the textDocument/completion request behavior described here. Determine whether client-side indentation for additionalTextEdits can be specified without ambiguity, and document the accepted protocol design and its completion semantics.