VBScript のプロパティ、Pattern プロパティ ?

Set r = New RegExp

str = "abc"
r.Pattern = "ab?"
Set Matches = r.Execute(str)
MsgBox Matches(0) ' ab

str = "abc"
r.Pattern = "ac?"
Set Matches = r.Execute(str)
MsgBox Matches(0) ' a

str = "abbbc"
r.Pattern = "ab?"
Set Matches = r.Execute(str)
MsgBox Matches(0) ' ab