[Silhouette]

For the US, IRS publications 515 and 519 clarify all that stuff. The IRS wants to tax "US Source Income", there are various criteria that define it.

Are we back to talking about sales or other revenue-based tax here? The major dispute we were originally talking about in this HN discussion was to do with where profits are declared and corporation tax or the equivalent is paid; I only mentioned the sales/VAT angle as an example of how easily tax rules can get complicated when you have to decide where some intangible thing happened.