VBScript のプロパティ、Pattern プロパティ \b

Set r = New RegExp

str = "abc"
r.Pattern = "\bc"
Set Matches = r.Execute(str)
MsgBox Matches.Count ' 0

str = "abc"
r.Pattern = "c\b"
Set Matches = r.Execute(str)
MsgBox Matches(0).FirstIndex ' 2