Is used to interpret the values not literally, and will take whatever its given and go through the implemented functions and processes that each value has
PHP code should be ran through web server applications, as it will show the result of the code's execution.
Incompatiable verisons play a role in how programs run, as some older functions way be deprecated. Newer verisons have fixed bugs and issues, which it will likely cause errors if two different versions run together.
It will help further debug, allowing for further detail of a bug or problem that needs more investigation.
It is important to check the source of the HTML, as sometimes the website may not be updating correctly, or could be missing some code you've already implemented.
Acknowledging warnings and errors provided by the console is vital, as if they are ignored it could cause alot more problems than it should.
Taking breaks is important, as sometimes giving yourself fresh air or time to ponder can give enough room for an answer.
It is a superglobal array variable that stores the information about the server and environment.
Commonly used to help debug and determine certain properties.
An example below is the following usage of "HTTP_USER_AGENT". There are many other lists provided in PHP documentation.