[wp-hackers] What makes WP index a plugin?

[Arthur]

This seems like a goofy question, but I've ran into some problems, when 
creating both themes and plugins. When creating plugin from scratch, I 
put all the meta info required in empty file, name it like 
'plugin_name.php', go into WP dashboard, restart it - plugin not 
recognized. I go back, copy-paste the 'Hello, Dolly' plugin, rename it 
both in file name and in meta, delete all the content in file except 
meta comments, then go to WP dashboard, restart - and voila, new plugin 
appears.
So, what could this be all about?

Thanks in advance.