Limiting these statistics to the North American Numbering Plan Area, where PBX extensions are common in the real world, we can see that the informal syntax is the most common syntax, about twice as common as the standard E.123 format (in English, French, and Spanish):
| Syntax | Example | Prevalence |
|---|---|---|
| Informal North American | +1-905-688-5550x3369 |
183 |
| E.123 | +1-978-750-1900 ext. 4309 |
94 |
| Escaped semicolon | +1-802-464-1100\;ext=4697 |
66 |
| DIN 5008 | +1 410 235 8744-5 |
1 |
This syntax is spread across multiple metropolitan regions, suggesting organic usage. It’s prevalent across English- and French-speaking regions, though we have only one example from a Spanish-speaking region:
If we make the period in “ext.” optional and allow the plural form “exts.”, then the E.123 format rises to 150 occurrences, putting it in a close second, with a few occurrences in the Caribbean.
Although the E.123 format is standard globally, it’s too fragile and not as familiar. There are even more occurrences of this syntax if we allow for other typos. So we would have to be very fussy about how to format the “ext.” token in each language, only to turn around and tell data consumers they should accept any language’s abbreviation in that position.
I’m leaning toward documenting the unofficial x123 syntax as the preferred syntax for POIs within the NANPA, alongside the existing allowance for extra dashes in this same region. The guidance about DIN 5008 in German-speaking regions would remain unchanged. Are there any objections to this regionalized approach?