Why strings in $_POST can not contain a dot “.”?

[bugatino]

Basicaly the title say's it all. i had an hidden input on my page where i wanted to set the name to "some.major.uber.setting"for example:\[code\]<input type="hidden" name="some.major.uber.setting" value="http://stackoverflow.com/questions/3742653/dummy value" />\[/code\]and when i looked at the $_POST data it contained "some_major_uber_setting". Can anybody explain this behaviour