.net - Regular expression, split string by capital letter but ignore TLA

Question

I'm using the regex

System.Text.RegularExpressions.Regex.Replace(stringToSplit, "([A-Z])", " $1").Trim()

to split strings by capital letter, for example:

'MyNameIsSimon' becomes 'My Name Is Simon'

I find this incredibly useful when working with enumerations. What I would like to do is change it slightly so that strings are only split if the next letter is a lowercase letter, for example:

'USAToday' would become 'USA Today'

Can this be done?

EDIT: Thanks to all for responding. I may not have entirely thought this through, in some cases 'A' and 'I' would need to be ignored but this is not possible (at least not in a meaningful way). In my case though the answers below do what I need. Thanks!

Answer 1

((?<=[a-z])[A-Z]|[A-Z](?=[a-z]))

or its Unicode-aware cousin

((?<=p{Ll})p{Lu}|p{Lu}(?=p{Ll}))

when replaced globally with

" $1"

handles

TodayILiveInTheUSAWithSimon
USAToday
IAmSOOOBored

yielding

 Today I Live In The USA With Simon
USA Today
I Am SOOO Bored

In a second step you'd have to trim the string.