What syntax is this when rendering the template?

if ():
endif;

what is this grammar and how to find a manual? thank you

<div class="am-u-sm-9 am-u-end">
    <select name="category[parent_id]"
            data-am-selected="{searchBox: 1, btnSize: "sm"}">
        <option value="0"></option>
        <?php if (isset($list)): foreach ($list as $first): ?>
            <option value="<?= $first["category_id"] ?>">
                <?= $first["name"] ?></option>
        <?php endforeach; endif; ?>
    </select>
</div>
Nov.23,2021
MySQL Query : SELECT * FROM `codeshelper`.`v9_news` WHERE status=99 AND catid='6' ORDER BY rand() LIMIT 5
MySQL Error : Disk full (/tmp/#sql-temptable-64f5-1b2c01a-2b332.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1b2c01a-2b332.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
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