Modifier Reference

Modifiers transform the output of an expression. They are applied using the pipe operator | and can be chained left to right.

{{ value | modifier_one | modifier_two arg="foo" }}

Note: Modifiers are the outermost operation in a pipeline. You cannot use dot notation to access properties on a modifier’s output (e.g., | get_post.title is invalid). Wrap in parentheses instead: (post.meta.id | get_post).title.

Positional vs. Named Arguments

Most modifiers accept both positional and named argument styles:

Modifiers supporting both styles and their argument names:

String Modifiers

upper / uppercase

Converts a string to UPPERCASE.

{{ user.name | upper }}
→ "JANE DOE"

lower / lowercase

Converts a string to lowercase.

{{ post.title | lower }}
→ "my post title"

upper_first / capitalize

Capitalizes the first character of every word in a string.

{{ post.meta.subtitle | upper_first }}
→ "Breaking News"

kebab

Converts a string to a URL-safe slug via WordPress’s sanitize_title(). Useful for generating CSS class names or URL slugs from dynamic values.

{{ post.title | kebab }}
→ "my-post-title"

truncate

Cuts a string to a maximum character length. Appends a suffix (default …) when truncation occurs. Length and suffix can both be passed positionally or via their named keys.

{{ post.excerpt | truncate 120 }}
{{ post.excerpt | truncate 120 '...' }}
{{ post.excerpt | truncate length=120 suffix='...' }}

trim

Strips leading and trailing whitespace. Pass an optional character mask positionally or via the named chars key to strip specific characters instead.

{{ post.meta.url | trim }}
{{ post.meta.url | trim '/' }}
{{ post.meta.url | trim chars='/' }}

replace

Finds all occurrences of a search string and replaces them with a replacement string. Supports positional or named arguments.

{{ post.title | replace 'Old' 'New' }}
{{ post.title | replace search='Old' replace='New' }}

esc_html

Explicitly escapes HTML entities in the output string.

{{ post.meta.user_input | esc_html }}

esc_attr

Escapes a value for safe use inside HTML attributes such as title, alt, or value.

{{ post.excerpt | esc_attr }}

raw

Marks a string as safe HTML, bypassing the default htmlspecialchars escaping path. Output is still filtered through wp_kses_post to strip dangerous tags like <script>.

{{ post.meta.html_content | raw }}

Use raw instead of triple-brace {{{ }}} syntax inside Gutenberg RichText — the triple-brace syntax is not supported there.

render

Recursively parses any {{ }} expressions found within the input string. Useful when expression strings are stored in post meta.

{{ post.meta.dynamic_template | render }}

Date Modifiers

date

Formats a date value using a PHP date format string. If no format is provided, the WordPress date_format site option is used as the default.

{{ post.date | date "F j, Y" }}
→ "February 24, 2026"

{{ "now" | date "Y-m-d" }}
→ "2026-02-24"

Logic Modifiers

default

Returns the provided fallback if the value is empty, null, or false.

{{ post.meta.subtitle | default "No subtitle provided" }}

if

The piped input value is treated as the condition. If truthy, returns the then argument; otherwise returns the else argument (or null if omitted).

{{/* Show label if badge_label is truthy */}}
{{ post.meta.badge_label | if then=post.meta.badge_label }}

{{/* Show label only if the user is logged in */}}
{{ user.is_logged_in | if then=post.meta.badge_label }}

match

Maps the incoming value to a corresponding output using named key=value pairs. Supports a built-in default argument as a fallback.

{{ post.meta.card_type | match event="Workshop" course="Academy" news="Alert" default="Resource" }}

Numeric matching: match uses loose comparison, so an integer value like 42 will correctly match a string case key of "42".

Data Modifiers

get_post

Hydrates a WP_Post object from a post ID. Use parentheses to access properties on the result, or chain the prop modifier to avoid wrapping the whole expression in parentheses.

{{ (post.meta.featured_post_id | get_post).title }}

{{/* Equivalent using prop — useful in longer pipelines */}}
{{ post.meta.featured_post_id | get_post | prop 'post_title' }}

prop

Accesses a named property on the pipeline value after a data-hydration modifier like get_post or get_user. The property name is resolved through the same Context::access() resolver used for dot-notation, so alias mappings (e.g. title → post_title) are fully supported.

{{ post.meta.featured_post_id | get_post | prop 'title' }}
{{ post.meta.author_id | get_user | prop 'email' }}

Tip: prop is the recommended alternative to wrapping the whole expression in parentheses when you only need a single property from the hydrated object.

resolve

Alias for get_post. Useful when the intent reads more naturally as “resolve this ID”.

{{ (post.meta.related_id | resolve).title }}

get_user

Hydrates a WP_User object from a user ID. Same pipeline limitation as get_post — property access via dot notation on the output is not supported.

{{ post.meta.assigned_to | get_user }}

get_meta

Fetches a single meta value by key from a post ID.

{{ post.id | get_meta key="custom_flag" }}

map

Extracts a specific key from every item in an array. Useful for arrays of associative data.

Note: map excludes WP_Post and WP_User objects for security — use get_meta for post-level data instead.

{{ post.meta.amenities | map key="label" | join ", " }}

Join Modifier

join

Joins an array of values into a string with a separator. Accepts the separator positionally or as the named glue argument.

{{ post.tags | join ", " }}
→ "WordPress, Gutenberg, Expressions"

Security & Protected Data

The engine proactively blocks access to sensitive data at the resolver level — these restrictions cannot be bypassed by the expression author.

Protected meta keys: Both post.meta property access and the get_meta modifier automatically deny any key that starts with an underscore (WordPress’s convention for private meta, e.g., _edit_lock) as well as explicitly sensitive keys like session_tokens.

User data restrictions: The user context proxy blocks access to database-prefixed role and capability keys (e.g., wp_capabilities, wp_user_level) to prevent leaking site-level permissions through expressions.

HTML output: All expression output is HTML-escaped by default via htmlspecialchars. The raw modifier bypasses this path but still runs through wp_kses_post — tags like <script> and <iframe> are stripped regardless.