To you both, I'll try to clarify a few things:
We're talking about 3 different things here:
1) Font Suitcase: a file with a file type of 'FFIL' and creator code of 'DMOV'. It acts as container file to hold Bitmap fonts (single A in OS 9) and/or TrueType fonts (triple A in OS 9).
2) Bitmap font: a file with a file type of 'ffil' and creator code of 'DMOV'. In OS 9, this file would have a single A icon. Internally, this font contains a 'FOND' (Font Family) resource which contains general information about the font family the font belongs to, and an 'NFNT' (New FONT) resource, which contains information about the particular font face, including the bit image of the glyphs in the font.
3) TrueType font: a file with a file type of 'tfil' and a creator code of 'DMOV'. In OS 9, this file would have a triple A icon. Internally, this font contains a 'FOND' (Font Family) resource which contains general information about the font family the font belongs to, just as it does in a Bitmap font. A TrueType font differs in that the second resource type it contains is an 'sfnt' (Spline font?) resource, which contains the vector information of the font outlines. Since this resource is contained within the same file, there is no need for an external secondary file as there is with PostScript Type 1 fonts.
Ordinarily in OS X, you don't usually see either Bitmap fonts or TrueType fonts, as they're usually contained within a "Font Suitcase".
I will have to do some further research, but I think these "loose" Bitmap fonts and TrueType fonts should be usable in some manner, provided the Bitmap font is accompanied by the corresponding outline fonts. The reason I say that is that, internally, there is actually very little difference between a single bitmap font that is loose and one that is inside a Font Suitcase. In both cases, you simply have a file that contains a 'FOND' resource and an 'NFNT' resource. The only real difference is that the files have a different file type ('ffil' vs. 'FFIL'). There might be a difference when there are a combination of bitmap fonts in a font suitcase (not of different sizes, but of different styles). What I mean is, I'm not sure how OS X would treat having "Helvetica 10", "Helvetica Bold 10", "Helvetica Oblique 10", and "Helvetica Bold Oblique 10" as loose files vs. having them in a single suitcase.
Anyway, this brings us to the issue about the "Font.mdimporter Document". Kurt, this is probably where not having Tiger will effect the way you interpret what this document is. I'm pretty sure that loose Bitmap fonts and/or loose TrueType fonts (with the file type and creator codes I mentioned earlier) might be referred to as "Font.mdimporter Documents". That's because there is no other application on the system that "claims" those combinations of file types and creator codes. Font Book doesn't, but the /System/Library/Spotlight/Font.mdimporter Spotlight importer does claim some information about these fonts.
The CoreTypes.bundle ("/System/Library/CoreServices/CoreTypes.bundle/Contents/Info.plist") declares all three items I mentioned above to be mapped to the same Uniform Type Indicator (UTI) of "com.apple.font-suitcase" See
System-Declared Uniform Type Identifiers.
I will have to double check on another Mac, as on mine (which has the beta of Font Finagler with the font suitcase editing feature on it, which claims the document types of Font Suitcase, Bitmap font, and TrueType font), the items are treated as above and are referred to as Font Suitcase, Bitmap font, and TrueType font.
Anyway, I hope that makes some sense.