Description:
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I propose the ability to create "macros" that can be used in the HTML (outside of the PHP start and end tags, <?php and ?>).

This will facilitate using PHP in systems oriented to web site builders who lack knowledge of PHP, but need to use certain interactive features.

The below example creates a macro USERNAME which can be inserted into HTML to reflect the current site user's name.
However, macros could perhaps also be used to create forms, e.g. by defining a macro "FORM". 
Also, if macros could be defined so as to take arguments, they would be even more powerful.

Reproduce code:
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<?php

global $USERNAME;
$USERNAME = "John";

macro USERNAME {
  global $USERNAME;
  echo $USERNAME;
}

?>

Hello!<br>
Your name is USERNAME.<br>
Bye!

Expected result:
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Hello!
Your name is John.
Bye!