ZWJ structure is inspected without assuming glyph support
Joined parts, modifiers and Emoji 17 RGI status are reported separately from whether the current platform renders one combined glyph.
A ZWJ sequence is more than visible glyph count
Emoji can combine multiple Unicode code points with the zero-width joiner, variation selectors, skin-tone modifiers, and other characters into one displayed grapheme. A sequence that looks like a single symbol may therefore contain several code points, and the same sequence can render differently across operating systems and font versions.
Inspect structure separately from appearance
Use the code-point breakdown to confirm where U+200D JOINER characters and modifiers occur. Then test the exact sequence on the platforms you support, because structural validity does not guarantee that every renderer has a dedicated combined glyph. Copying, deleting, cursor movement, string length, database limits, and regular expressions may also operate on code units or code points rather than user-perceived emoji clusters.