query on defining xml tags

Hi,
This is a very basic question on defining xml tags. I'm not sure if
this is the right forum to ask.

Anyway, <1-1>data</1-1> Is this not the proper syntax for xml tags as
per the XML standards. I could parse the xml tags <if1-1>data</if1-1>,
but not the previous one. I would like to know about this.

Thanks
Senthil