Description:
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Constants can be defined with invalid characters in the name. The documentation is correct but there seems to be no validation that matches the docs when the constant's name is assigned to zend_constant.name

According to the docs on Constants:

The name of a constant follows the same rules as any label in PHP. A valid constant name starts with a letter or underscore, followed by any number of letters, numbers, or underscores. As a regular expression, it would be expressed thusly: [a-zA-Z_\x7f-\xff][a-zA-Z0-9_\x7f-\xff]*

Test script:
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<?php

define('/', 'slash');

echo constant('/'); // works

echo /; // parse error as expected

?>

Expected result:
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define() should throw an error stating that the constant name has invalid characters in it