Why is a tags first letter in lower case?

1. Should tags be uppercase or lowercase?
2. Should tags be lowercase?

Should tags be uppercase or lowercase?

Tag casing doesn't matter. Capitalize or not as you choose. I usually capitalize, but since there's no right or wrong, do whatever's more convenient. Much better to spend time figuring out the nature of your tag organizational scheme if you're going to use tags to organize.

Should tags be lowercase?

While it is valid to write tags using any case you prefer when writing HTML 5, the convention is to use all lowercase for tags and attributes.