PHP short marker <?? > < with long markers;? The difference between php?>

The so-called identifier refers to the name of the variable.

The names of functions and classes are also identifiers.

PHP Rules for identifiers:

• Identifiers can be any length of letters, numbers, underscores, and do not begin with a number.

• Identifiers in PHP are case-sensitive, but the function name is an exception.

• The variable name can be the same as the function name. But should be avoided as far as possible.

• You cannot create a function with the same name as an existing function.

Short marks are used only to output variables or expressions, and the general usage is

<?= $a? ><?= (expression)?>

is equivalent to

<?php echo $a? ><?php echo (expression)?>

such as if, for and other structures.
If you write

<?if (...?). >

He's going to turn you into

<!--if (...-->

So write the program must use a long mark, the HTML inserted in the output will be marked with a short.