Entering regular expression in TextField

I'm using a TextField in SwiftUI to enter regular expressions in an iOS app. But when I enter three dots (...) into the field, they are automatically converted to a single Unicode character. This does not create the regular expression I want to use. I've added

.disableAutocorrection(true)

to the text field, but the auto substitution still occurs. Is there some way I can prevent this from happening?