Regular Expression: BRE vs. ERE?

[Paul Gilmartin]

I read in Regular expressions (string, string1):
<https://www.ibm.com/docs/en/zos/3.1.0?topic=string-regular-expressions-string1>
... matching a basic or extended regular expression.

How can users indicate whether they are using BRE or ERE syntax?

Why does the list of special characters below show those only
for extended regular expressions and not also those for
basic regular expressions?

Why does Appendix C of the UNIX System Services Command Reference
show oedit, which is a wrapper for ISPF Edit, as supporting only
BRE and not also ERE, and not show obrowse at all?

(I've already submitted a Feedback on part of this.)

--
Thanks,
gil