Prescriptivists would say it should be "one [..] upon his", but the author may wish to avoid using gender specific pronouns and is thus using the singular "their" instead.
I accept both points. I was reflecting on usage I have seen in late Victorian/Edwardian sources. That seemed to fit with the style of the text (although not the visual presentation of the page).
PS: 'Spiffing' is later and the Jeeves references in the HTML markup point to 1920s. Biggles. Biplanes.
> I personally rather regret the automatic recitation of Arne's ditty when visiting the page.
Possibly the first time I have appreciated auto-play music on a site, made me laugh. And now it's put me into a baroque mood which is always a good thing.
"...one must check whether one has PHP 5.2 (or newer) installed upon their Internet server..."
Should this not be 'one's Internet server'?
"Something our primitive stateside friends can understand"
What is this 'stateside' you speak of, Sir? Our Colonial Cousins may also resent the adjective that has been applied.
I personally rather regret the automatic recitation of Arne's ditty when visiting the page.