NSAttributedString中的NSOriginalFont属性是什么？

Question

NSOriginalFont属性是什么？为什么我的属性字符串包含它？

s{
    NSColor = "NSCalibratedWhiteColorSpace 0 1";
    NSFont = "\"ABeeZee-Regular 19.00 pt. P [] (0x608002047b30) fobj=0x128b84cd0, spc=5.70\"";
    NSParagraphStyle = "Alignment 2, LineSpacing 0, ParagraphSpacing 0, ParagraphSpacingBefore 0, HeadIndent 0, TailIndent 0, FirstLineHeadIndent 0, LineHeight 0/0, LineHeightMultiple 0, LineBreakMode 0, Tabs (\n    28L,\n    56L,\n    84L,\n    112L,\n    140L,\n    168L,\n    196L,\n    224L,\n    252L,\n    280L,\n    308L,\n    336L\n), DefaultTabInterval 0, Blocks (\n), Lists (\n), BaseWritingDirection -1, HyphenationFactor 0, TighteningForTruncation NO, HeaderLevel 0";
}da{
    NSColor = "NSCalibratedWhiteColorSpace 0 1";
    NSFont = "\"ABeeZee-Regular 19.00 pt. P [] (0x608002047b30) fobj=0x128b84cd0, spc=5.70\"";
    NSOriginalFont = "\"HelveticaNeue 19.00 pt. P [] (0x60000045bf60) fobj=0x128b022c0, spc=5.28\"";
    NSParagraphStyle = "Alignment 2, LineSpacing 0, ParagraphSpacing 0, ParagraphSpacingBefore 0, HeadIndent 0, TailIndent 0, FirstLineHeadIndent 0, LineHeight 0/0, LineHeightMultiple 0, LineBreakMode 0, Tabs (\n    28L,\n    56L,\n    84L,\n    112L,\n    140L,\n    168L,\n    196L,\n    224L,\n    252L,\n    280L,\n    308L,\n    336L\n), DefaultTabInterval 0, Blocks (\n), Lists (\n), BaseWritingDirection -1, HyphenationFactor 0, TighteningForTruncation NO, HeaderLevel 0";
}dd{
    NSColor = "NSCalibratedWhiteColorSpace 0 1";
    NSFont = "\"HelveticaNeue 19.00 pt. P [] (0x60000045bf60) fobj=0x128b022c0, spc=5.28\"";
    NSParagraphStyle = "Alignment 2, LineSpacing 0, ParagraphSpacing 0, ParagraphSpacingBefore 0, HeadIndent 0, TailIndent 0, FirstLineHeadIndent 0, LineHeight 0/0, LineHeightMultiple 0, LineBreakMode 0, Tabs (\n    28L,\n    56L,\n    84L,\n    112L,\n    140L,\n    168L,\n    196L,\n    224L,\n    252L,\n    280L,\n    308L,\n    336L\n), DefaultTabInterval 0, Blocks (\n), Lists (\n), BaseWritingDirection -1, HyphenationFactor 0, TighteningForTruncation NO, HeaderLevel 0";
}