MS Access 2007 Curiosity Question On Alias Names

I tried to use the following line in an Access query

Code:

---

TableName.Field Name _
AS [Percentile Ranking Quality In Use Overall (Excluding Pr w/<3 metrics)],

---

It threw and "Not A Valid Alias Name" error at me.

I googled the error and discovered that if I put the exact same alias name in the caption of the field in design mode, it worked just fine.

Why does it work in the fields caption property, but not in a query? :confused:

(BTW: This did work in the query

Code:

---

TableName.Field Name _
AS [Percentile Ranking Quality In Use Overall (Excluding Pr w/<3],

---

But if I added the word "metrics" it threw the error.)

As I mentioned, I have fixed the problem by using the field's caption property, but I'm very curious as to why the error is thrown in the first place.

Anyone have any ideas?