Strict tags

By default, Mustache ignores missing tags. A missing variable renders as an empty string, a missing section renders nothing, and a missing partial is logged but otherwise skipped.

Output coercion is strict by default, matching previous Mustache.php behavior. Non-scalar, non-stringable output values throw a clear RuntimeException instead of relying on PHP string coercion failures.

Set the strict_tags engine option to make selected missing tags fail instead:

$mustache = new \Mustache\Engine([
    'strict_tags' => \Mustache\Engine::STRICT_INTERPOLATION | \Mustache\Engine::STRICT_PARTIALS,
]);

Set strict_tags to true to enable all strict checks, or false to disable them all, including strict output coercion.

Available checks

• STRICT_INTERPOLATION: missing interpolation tags like {{ name }} throw UnknownVariableException.
• STRICT_SECTIONS: missing section and inverted section tags like {{# items }} and {{^ items }} throw UnknownVariableException.
• STRICT_PARTIALS: missing partial templates like {{> sidebar }} throw UnknownTemplateException.
• STRICT_PARENTS: missing parent templates like {{< layout }} throw UnknownTemplateException.
• STRICT_EXTRA_BLOCKS: extra inheritance block overrides throw UnknownBlockException when they cannot be matched to a rendered parent template.
• STRICT_COERCION: non-scalar, non-stringable output values throw RuntimeException. This is enabled by default.
• STRICT_ALL: enables every strict check available in this release.

To relax output coercion while keeping other checks strict, pass a bitmask that excludes STRICT_COERCION.

Extra block overrides

STRICT_EXTRA_BLOCKS validates block overrides as parent templates are resolved for rendering.

An override is accepted when the resolved parent declares that block, even if the block itself is inside a false section and does not render:

{{! layout }}
{{# show_title }}
  {{$ title }}Default title{{/ title }}
{{/ show_title }}

{{! page }}
{{< layout }}
  {{$ title }}Page title{{/ title }}
{{/ layout }}

If show_title is false, this renders without throwing because layout still declares the title block.

If a parent tag is skipped by a section or another runtime condition, Mustache does not validate block overrides against templates on that skipped path:

{{! wrapper }}
{{# use_layout }}
  {{< layout }}{{/ layout }}
{{/ use_layout }}

{{! page }}
{{< wrapper }}
  {{$ typo }}Extra block{{/ typo }}
{{/ wrapper }}

If use_layout is false, layout is never resolved, so STRICT_EXTRA_BLOCKS does not throw for typo.

Dynamic names

Dynamic partial and parent names are resolved at render time. With the relevant strict check enabled, a missing dynamic name variable throws UnknownVariableException; a resolved template name that cannot be loaded throws UnknownTemplateException.

For extra block checks, dynamic parents follow the same rule as static parents: validation happens after the concrete parent template is resolved for rendering.