`{`

... `}`

or `\{`

... `\}`

)
If the syntax bit `RE_INTERVALS`

is set, then Regex recognizes
interval expressions. They repeat the smallest possible preceding
regular expression a specified number of times.

If the syntax bit `RE_NO_BK_BRACES`

is set, ‘`{`’ represents
the open-interval operator and ‘`}`’ represents the
close-interval operator ; otherwise, ‘`\{`’ and ‘`\}`’ do.

Specifically, supposing that ‘`{`’ and ‘`}`’ represent the
open-interval and close-interval operators; then:

`{`

`count``}`

- matches exactly
`count`occurrences of the preceding regular expression. `{`

`min``,}`

- matches
`min`or more occurrences of the preceding regular expression. `{`

`min``,`

`max``}`

- matches at least
`min`but no more than`max`occurrences of the preceding regular expression.

The interval expression (but not necessarily the regular expression that contains it) is invalid if:

`min`is greater than`max`, or- any of
`count`,`min`, or`max`are outside the range zero to`RE_DUP_MAX`

(which symbol`regex.h`defines).

If the interval expression is invalid and the syntax bit
`RE_NO_BK_BRACES`

is set, then Regex considers all the
characters in the would-be interval to be ordinary. If that bit
isn't set, then the regular expression is invalid.

If the interval expression is valid but there is no preceding regular
expression on which to operate, then if the syntax bit
`RE_CONTEXT_INVALID_OPS`

is set, the regular expression is invalid.
If that bit isn't set, then Regex considers all the characters—other
than backslashes, which it ignores—in the would-be interval to be
ordinary.