Do you want all rules to be performed simultanuously? Or sequentially? That is, if I have "foo{space}{tab}{space}bar" should that result in "foo{space}{space}bar", or in "foo{space}bar"? Rule 2 says repeating spaces should be collapsed, but the original string doesn't have repeated spaces - they only repeat after rule 1 has been applied.

Assuming rules should be applied in order:

    no warnings "uninitialized";
    s/([ \n])|\s/$1/g;
    s/(\s)\K\1+//g;
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If they apply all at once:

    no warnings "uninitialized";
    s/([ \n])\1+|\s/$1/g;
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(None of the snippets above were tested).