Clarification on "filter_palette_zero"

[MasterInQuestion]

    For Palette images and those of < 8bpc (bit-depth per component):
    https://github.com/lvandeve/lodepng/blob/87032dd9c379892e08bba71c647bdaca793aee3c/lodepng.cpp#L5914-L5928
    https://github.com/lvandeve/lodepng/blob/87032dd9c379892e08bba71c647bdaca793aee3c/lodepng.h#L823-L827

    The PNG standard didn't suggest so:
    https://www.w3.org/TR/png/#12Filter-selection
    ; it's suggested by the "libpng" book...
    http://www.libpng.org/pub/png/book/chapter09.html#INDEX-682

    Note there are some malapropos ideas in the PNG book.
    Notably:
    "So how does an encoder actually choose the proper filter for each row? Testing all possible combinations is clearly impossible: ..."
<^>    It's actually suggested by the PNG standard as the optimal optimization method...
    If speed is not of primary concern.
    .
    "The first rule is that filters are rarely useful on palette images, so don't even bother with them."
<^>    No filtering does not necessarily cause best compression in such cases. (mere mostly)
    It's mostly as a performance optimization.
    .
    "The theory, to some extent based on empirical evidence, is that switching filters too often can have a deleterious effect on the main compression engine."
<^>    Data, are no more than data. It is all upon: the interpretation.
    For any proper general purpose compressor, this shouldn't make a difference.
    .
    “In particular, you cannot treat color values and transparency values as if they are separate, unrelated entities.
    Attempting to partition the palette into a "color part" and a "transparent part":
    Makes no more sense, than attempting to partition a standard RGB palette into: red, green, and blue parts.”
<^>    https://www.awaresystems.be/imaging/tiff/tifftags/planarconfiguration.html
    https://gist.github.com/Jim-Bar/3cbba684a71d1a9d468a6711a6eddbeb#packed-planar-and-semi-planar
    Planar in certain cases may be noticeably more compressible than Packed.
    (the opposite may occur too, much dependent on the input)