Merge tags for developers

POM HTML templates use:

{{tag_name attribute="value"}}

Attributes may be double-quoted, single-quoted or unquoted where safe. Use literal delimiters for values containing spaces, quotes, HTML or nested tags:

{{translatable_string text=%%A label with "quotes"%%}}

Conditional blocks use:

{{if meta="featured" value="not_empty"}}
    …
{{else}}
    …
{{/if}}

Template contexts have different catalogs:

• Archive contract / complete archive reference
• Feed contract / complete feed reference
• Single contract / complete single reference

Do not evaluate arbitrary PHP or add an undocumented generic expression language. New merge tags need a named parser/renderer contract, attribute validation, context-aware escaping, translation behavior, empty-value behavior and public documentation.