finance conventions

I've asserted at various times that finance is easy, so they have to invent strange conventions to make it hard.[1]  In his Tuesday column, Matt Levine gave an example, sort of:

The difference is that if you buy a $100 Venezuela 9.25 percent bond a day before the semiannual interest payment is due, and the price is $20, then if it trades clean you pay the seller $20 for the bond plus like $4.60 of accrued interest, while if it trades flat you just pay the seller the $20.

This is correct in some sense, but the emphasis is not what I think a person not steeped in finance conventions would find natural; the way I would put it is

The difference is that if you buy a $100 Venezuela 9.25 percent bond a day before the semiannual interest payment is due, and you want to agree to a price of like $24.60, then if it trades clean you call the price $20 with like $4.60 of accrued interest, while if it trades flat you just call the price $24.60.

The effect of "accrued interest" is to smooth out price drops; for a bond trading at par, the day before a $2 payment, you'll pay $102 (more or less), while the next day you'll pay $100 (because you aren't getting the $2 payment, the seller is), and if it trades "clean" then, by convention, you call it $100 on both days. Stock traders just accept that the day a stock goes "ex-dividend" the price drops, and I think in a day when traders are sitting in front of computers, it's more straightforward to call the price the price instead of adopting weird rules to make it seem to behave differently from how it actually does.

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[1] The hardest parts of finance, though, are law.  Conventions are second.