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Output Filters

Output filters modify the final script or link tag.

<?php

use SymPress\Assets\Script;

$script = (new Script('site', plugin_dir_url(__FILE__) . 'assets/site.js'))
    ->withAttributes(['crossorigin' => 'anonymous']);

Included Filters

• AttributesOutputFilter sets additional attributes.
• InlineAssetOutputFilter emits small, allowed CSS or JS files inline.
• AsyncStyleOutputFilter loads non-critical CSS through preload.

Style::preload() requests AsyncStyleOutputFilter. Supply the page's intentional per-request CSP nonce through sympress_assets_csp_nonce (value, asset). When a nonempty nonce and WP_HTML_Tag_Processor are available, output contains a preload link plus a nonce-bearing script using addEventListener, with no onload attribute. The nonce must match the page's script-src policy; putting a nonce on a link does not authorize inline event handlers. The script handles already completed/cache-hit loads, and a noscript copy keeps the original stylesheet. Existing media, integrity, crossorigin and fetchpriority are preserved. Without a nonce the original blocking stylesheet is returned, so strict script-src-attr 'none' remains supported.

Inline files must satisfy the allowed canonical path/extensions and 32KB limit, including the actual read bytes. Raw JavaScript containing closing/opening script prefixes, HTML comment openings, or U+2028/U+2029 falls back to its external tag. There is no semantics-preserving universal rewrite for strings, regexps and tagged templates; external fallback keeps the exact program bytes. CSS closing style prefixes are escaped case-insensitively. Inline output retains nonce and removes external-only integrity/src/loading attributes.

For scripts, AsyncScriptOutputFilter and DeferScriptOutputFilter are deprecated. Use Script::async() or Script::defer() instead.

Custom Filter

<?php

use SymPress\Assets\Asset;
use SymPress\Assets\Script;

$filter = static function (string $html, Asset $asset): string {
    return str_replace('></script>', ' data-handle="' . esc_attr($asset->handle()) . '"></script>', $html);
};

$script = (new Script('site', plugin_dir_url(__FILE__) . 'assets/site.js'))
    ->withFilters($filter);

Supplied SRI and request snapshots

Loader configuration and dependency JSON may provide integrity (space-separated sha256/384/512 base64 digests) and crossorigin (anonymous/use-credentials). Digest format/decoded length is validated and anonymous is the default. Hashes must come from a trusted build for the exact bytes served. The library does not synthesize integrity from URLs/versions or fetch remote files; no remote integrity guarantee is possible without supplied build metadata. Inline tags omit external integrity.

RequestFiles shares canonical path/stat/content/JSON snapshots across assets and loaders. Repeated reads and missing paths reuse a request snapshot, while allowed root policy decisions remain local to their policy context. Call SymPress\Assets\IO\RequestFiles::reset() at every request boundary in a long-running worker, and recreate per-request asset objects. Normal PHP request teardown already clears this memory. New/changed manifests and symlink targets are observed after reset; do not modify build files partway through a request. PHP dependency execution remains separately opt-in and size-bounded.

CSP preload requires an intentional page nonce via sympress_assets_csp_nonce; without it CSS stays blocking. Supplied build SRI and request-scoped file snapshots are documented in output filters. Long-running workers must reset RequestFiles and recreate request asset objects at each boundary.