The unfiltered ones include, incredibly, the private use area of Unicode. You know, the code points that might show up as any symbol at all depending of the font?

About a year ago, (https://news.ycombinator.com/item?id=22741817) someone here used what they thought was the Apple logo symbol, but some fonts (which follow the ConScript (unofficial) Unicode Registry for private use characters) might show a KLINGON MUMMIFICATION GLYPH instead!