There is a piece of common wisdom that says that you can remember about seven things at a time in your short term memory (Human register set I guess). So, given that limitation there is no reason at all to declare all your variables in one place at the start of anything - you'll forget them anyway.

However, the much more important reason for declaring a variable as late as possible is that it is much easier to see where and how it is used. There is no need to know about a variable until the variable is needed so there is no need to burden the limited storage facility of the reader of your code by introducing variables before they are needed. Bottom line: Declaring variables early doesn't help anyone.

There is nothing wrong with learning about the 'raw "under the covers" way to do it', but there are some tasks such as parsing generally, and parsing markup in particular that are much more subtle than one might first think. It is well worth being aware of the modules that are available for performing such tasks after your initial foray into rolling your own.