Regex matches the string that is the part of an explicit string.
e.g.
an explict string
hello world!
matches
h
he
...
hello wor
hello worl
hello world!
not matches
a
ah
ha
hallo
hbbbo asrld!
hbbboaasrld!
Thbbboaasrld!
As shown below
/^h(e(l(l(o( (w(o(r(l(d(!?)?)?)?)?)?)?)?)?)?)?)?$/
but it is not convenient for modification and expansion.
Is there a simpler expression?