<p>Is there a difference between <code>NULL</code> and <code>null</code> in PHP? Sometimes they seem to be interchangeable and sometimes not.</p>

<p>edit: for some reason when I read the documentation linked to in the answer (before posting this question) I read it as "case sensitive" instead of "case insensitive" which was the whole reason I posted this question in the first place...</p>

[{'answer_id': 8869, 'author': 'mbillard', 'author_id': 810, 'author_profile': 'https://Stackoverflow.com/users/810', 'pm_score': 8, 'selected': True, 'text': '<p>Null is case insensitive.</p>\n\n<p>From the <a href="http://ca3.php.net/manual/en/language.types.null.php" rel="noreferrer">documentation</a>:</p>\n\n<blockquote>\n  <p>There is only one value of type null, and that is the <strong>case-insensitive</strong> keyword NULL.</p>\n</blockquote>\n'}, {'answer_id': 16629586, 'author': 'Desolator', 'author_id': 326904, 'author_profile': 'https://Stackoverflow.com/users/326904', 'pm_score': 4, 'selected': False, 'text': '<p>There is no difference. Same type just its a <strong>case insensitive</strong> keyword. Same as <code>True</code>/<code>False</code> etc...</p>\n'}, {'answer_id': 70534304, 'author': 'RedDragonWebDesign', 'author_id': 3480193, 'author_profile': 'https://Stackoverflow.com/users/3480193', 'pm_score': 2, 'selected': False, 'text': '<p>Either will work. But the official PHP style guide, PSR-12, recommends lowercase.</p>\n<p><a href="https://www.php-fig.org/psr/psr-12/" rel="nofollow noreferrer">https://www.php-fig.org/psr/psr-12/</a>, Section 2.5</p>\n'}]
['https://Stackoverflow.com/questions/8864', 'https://Stackoverflow.com', 'https://Stackoverflow.com/users/58/']