Compliance and law
Taxable event
The event that triggers taxation. In several regimes, only the exit into money is one.
Identifying the applicable taxable event is the first thing to do when reading a tax regime. Some tax only disposal for legal tender or the purchase of goods; others also tax swaps between digital assets.
That single difference changes the record-keeping burden entirely. In the first case you track money in and money out. In the second, every asset-to-asset operation must be valued on the day it happens.