What is the DOM Core Level / Version Supported by PHP DOM?

Question

What is the DOM Core Version is Supported by PHP DOM? I can see there are many different ones listed like (list):

• Document Object Model (Core) Level 1 (via Document Object Model (DOM) Level 1 Specification)
• Document Object Model Core Level 2
• Document Object Model Core Level 3

Which one is supported?

Answer 1

PHP DOM Extension has the Document Object Model (Core) Level 1 feature. You can test for features that are implemented with a helper method and then testing for features and versions, here a summary for four features:

• One Core versions found: '1.0'.
• Four XML versions found: '2.0'; '1.0'; ''; NULL.
• Zero HTML versions found.
• Zero XHTML versions found.
• Zero XPath versions found.

This result combine with the specs is puzzeling if not esoteric. The Core Feature in Level 1.0 requires to return TRUE as well for a non-specified version (here: for '' and NULL), but as the results show, it does not. So even DOM Core Level 1 is announced as feature, it's also broken.

Also the XML Feature can not be level 2.0 if the Core feature of level 2.0 is not supported - and this is the case here, Core Level 2.0 is not a supported feature.

Features in DOM (source):

Exemplary Output of my example script:

Core Feature is in PHP DOMDocument implementation:

    1.) Core '3.0': FALSE
    2.) Core '2.0': FALSE
    3.) Core '1.0': TRUE
    4.) Core ''   : FALSE
    5.) Core NULL : FALSE

One Core versions found: '1.0'.

XML Feature is in PHP DOMDocument implementation:

    1.) XML '3.0': FALSE
    2.) XML '2.0': TRUE
    3.) XML '1.0': TRUE
    4.) XML ''   : TRUE
    5.) XML NULL : TRUE

Four XML versions found: '2.0'; '1.0'; ''; NULL.

HTML Feature is in PHP DOMDocument implementation:

    1.) HTML '3.0': FALSE
    2.) HTML '2.0': FALSE
    3.) HTML '1.0': FALSE
    4.) HTML ''   : FALSE
    5.) HTML NULL : FALSE

Zero HTML versions found.

XHTML Feature is in PHP DOMDocument implementation:

    1.) XHTML '3.0': FALSE
    2.) XHTML '2.0': FALSE
    3.) XHTML '1.0': FALSE
    4.) XHTML ''   : FALSE
    5.) XHTML NULL : FALSE

Zero XHTML versions found.

XPath Feature is in PHP DOMDocument implementation:

    1.) XPath '3.0': FALSE
    2.) XPath '2.0': FALSE
    3.) XPath '1.0': FALSE
    4.) XPath ''   : FALSE
    5.) XPath NULL : FALSE

Zero XPath versions found.

Example script:

<?php
/**
 * What is the DOM Core Version is Supported by PHP DOM?
 * @link http://stackoverflow.com/a/17340953/367456
 */

$dom = new DOMDocument();
$dom->loadXML('<root/>');

$versionsArray = ['3.0', '2.0', '1.0', '', NULL];
$features      = [
    # Document Object Model (DOM) <http://www.w3.org/DOM/DOMTR>
    'Core'  => $versionsArray,

    # Document Object Model (DOM) <http://www.w3.org/DOM/DOMTR>
    'XML'   => $versionsArray,

    # Document Object Model (DOM) Level 2 HTML Specification <http://www.w3.org/TR/DOM-Level-2-HTML/>
    'HTML'  => $versionsArray,
    'XHTML' => $versionsArray,

    # Document Object Model XPath <http://www.w3.org/TR/DOM-Level-3-XPath/xpath.html>
    "XPath" => $versionsArray,
];

const DISPLAY_TITLE   = 1;
const DISPLAY_DETAILS = 2;
const DISPLAY_SUMMARY = 4;
const DISPLAY_ALL     = 7;

dom_list_features($dom, $features);

function dom_list_features(DOMDocument $dom, array $features, $display = DISPLAY_ALL) {

    foreach ($features as $feature => $versions) {
        dom_list_feature($dom, $feature, $versions, $display);
    }
}

function dom_list_feature(DOMDocument $dom, $feature, array $versions, $display) {

    if ($display & DISPLAY_TITLE) {
        echo "$feature Feature is in PHP DOMDocument implementation:\n\n";
    }

    $found = [];

    foreach ($versions as $i => $version) {
        $result = $dom->implementation->hasFeature($feature, $version);
        if ($result) {
            $found[] = $version;
        }

        if ($display & DISPLAY_DETAILS) {
            printf("    %d.) $feature %' -5s: %s\n", $i + 1, var_export($version, true), $result ? 'TRUE' : 'FALSE');
        }
    }

    if ($display & DISPLAY_DETAILS) {
        echo "\n";
    }

    $formatter = new NumberFormatter('en_UK', NumberFormatter::SPELLOUT);
    $count     = ucfirst($formatter->format(count($found)));
    $found     = array_map(function ($v) {
        return var_export($v, TRUE);
    }, $found);

    if ($display & DISPLAY_SUMMARY) {
        printf("%s %s versions found%s.\n\n", $count, $feature, $found ? ': ' . implode('; ', $found) : '');
    }
}

Answer 2

The dom core version depends on the libxml2 version PHP is linked against. You can even replace the binary version of the library under the hood without need to recompile php. (That's hakish and limited I know, but once I did that because the debian lenny version of libxml2 had a bug)

For runtime detection of this features in PHP @hakre's answers is a nice snippet