Expressions & Syntax

Full reference for Unblock's expression syntax.

Unblock uses Twig expression syntax — widely used and well-documented.

Accessing Data

Use dot notation to access properties:

{{ post.title }}
{{ post.author.name }}
{{ site.name }}

Bracket notation for array elements or dynamic properties:

{{ array[0] }}
{{ array['key'] }}

Slice a string or a list with [offset:length]; either side can be left out:

{{ post.title[0:10] }}         <!-- First 10 characters -->
{{ items[1:2] }}               <!-- 2 items from the second -->
{{ items[:3] }}                <!-- First 3 items -->

A dot is already safe on a missing value: post.author.name gives nothing when there's no author. ?. is accepted too and works the same:

{{ post.author?.name }}
{{ post.thumbnail?.src }}

Method calls with arguments:

{{ post.date('F j, Y') }}
{{ user.avatar({size: 96}) }}
{{ post.meta('field_name') }}

After a filter, a dot or brackets read the filter's result, as in Twig:

{{ post.categories|first.name }}               <!-- Name of the first category -->
{{ get_posts({posts_per_page: 3})|last.title }}

Conditional Logic

Ternary Operator

{{ condition ? 'yes' : 'no' }}
{{ post.thumbnail ? 'Has image' : 'No image' }}
{{ user.id ? user.name : 'Guest' }}
{{ user.id ? 'Welcome!' }}                    <!-- Empty if guest -->

Without :, as in Twig, the value is an empty string when the condition is false: a ? b is a ? b : '', anywhere in an expression, such as (user.id ? 'Welcome') ~ '!'.

Fallback Operators

Operator	Name	Returns fallback when
??	Null coalescing	Value is null
?:	Elvis	Value is falsy (null, false, 0, '', [], a query without results)
|default	Default filter	Value is empty (like ?: but preserves 0)

{{ post.meta('subtitle') ?: 'No subtitle' }}
{{ post.meta('hero_image', {transform_value: true}) ?: post.thumbnail ?: '/default.jpg' }}
{{ post.comment_count ?: 'No comments' }}
{{ post.meta('subtitle')|default('No subtitle') }}
{{ request.get('page') ?? 1 }}

A missing custom field is an empty string, not null, as in WordPress and Timber: use ?: or |default to replace it. ?? suits values that are null when missing, such as a request parameter.

Comparison:

Value	??	?:	|default
'text'	'text'	'text'	'text'
null	fallback	fallback	fallback
false	false	fallback	fallback
0	0	fallback	0
''	''	fallback	fallback
[]	[]	fallback	fallback

Operators

Arithmetic

Operator	Description	Example
+	Addition	{{ 5 + 3 }} → 8
-	Subtraction	{{ 10 - 3 }} → 7
*	Multiplication	{{ 4 * 5 }} → 20
/	Division	{{ 20 / 4 }} → 5
%	Modulo	{{ 17 % 5 }} → 2
//	Floor division	{{ 17 // 5 }} → 3
**	Power	{{ 2 ** 3 }} → 8
..	Range	{{ (1..5)|join(', ') }} → 1, 2, 3, 4, 5

As in Twig, - also negates a value ({{ -post.meta('offset') }}), and subtracts without spaces too: {{ loop.length-1 }}.

Comparison

Operator	Description	Example
==	Equal	{{ a == b }}
!=	Not equal	{{ a != b }}
===	Identical	{{ a === b }}
!==	Not identical	{{ a !== b }}
<	Less than	{{ a < b }}
>	Greater than	{{ a > b }}
<=	Less or equal	{{ a <= b }}
>=	Greater or equal	{{ a >= b }}
<=>	Spaceship	{{ a <=> b }}

Logical

Operator	Description	Example
and	Logical AND	{{ a and b }}
or	Logical OR	{{ a or b }}
xor	Logical exclusive OR (true when exactly one side is true)	{{ a xor b }}
not	Logical NOT	{{ not a }}

String & Containment

Operator	Description	Example
~	Concatenation (cast to string)	{{ 'Hello ' ~ name }}
+	Concatenation, when a side is text	{{ post.title + ' - ' + site.name }}
starts with	Starts with test	{{ post.title starts with 'Hello' }}
ends with	Ends with test	{{ post.slug ends with '-draft' }}
in	Contains	{{ 'a' in ['a', 'b'] }}
not in	Not contains	{{ 'c' not in ['a', 'b'] }}

+ adds numbers and numeric strings, as in Twig: a custom field holding 5 plus 1 gives 6. With text on either side, it concatenates. ~ always concatenates.

Tests

Tests check a property of a value with is, or is not to negate:

Test	Description	Example
is defined	Value is not null	{{ user.id is defined }}
is empty	Value is empty (null, false, '', [], a query without results)	{{ post.meta('subtitle') is empty }}
is null / is none	Value is exactly null	{{ post.thumbnail is null }}
is even	Number is even	{{ loop.index is even }}
is odd	Number is odd	{{ loop.index is odd }}
is iterable	Value can be looped over	{{ post.tags is iterable }}
is sequence	Value is a list (sequential array)	{{ items is sequence }}
is mapping	Value is a map (keyed array or object)	{{ data is mapping }}
is divisible by(n)	Number divides evenly by n	{{ loop.index is divisible by(3) }}
is same as(x)	Strictly identical, type and value	{{ post.id is same as(1) }}

Negate any test with is not:

{{ post.thumbnail is not empty }}
{{ loop.index is not divisible by(2) }}

Operator Precedence

From lowest to highest priority, in Twig 4's order (Twig 3 gives the same results, except in the combinations it deprecates):

1. ? — Ternary
2. ??, ?: — Fallback
3. or — Logical OR
4. xor — Logical exclusive OR
5. and — Logical AND
6. ==, !=, ===, !==, <, >, <=, >=, <=>, in, not in, starts with, ends with — Comparison
7. .. — Range
8. ~ — Concatenation
9. +, - — Addition / Subtraction
10. *, /, %, // — Multiplication / Division
11. not — Logical NOT
12. is, is not — Tests
13. ** — Power (right-associative)
14. | — Filter
15. -, + — Negation, except before **: as in Twig, -2 ** 2 is -(2 ** 2), so -4; write (-2) ** 2 for 4
16. ., [] — Attribute access, also after a filter

{{ (a + b) * c }}
{{ (value ?? 'default')|upper }}
{{ (post.comment_count ?: 0) + 1 }}
{{ post.title|upper == 'HELLO' }}             <!-- Filter binds before comparison -->
{{ 'Total: ' ~ price + 1 }}                   <!-- Adds before joining -->
{{ not post.meta('subtitle') is empty }}      <!-- not (… is empty) -->

Literals

{{ 'single quotes' }}          {{ "double quotes" }}
{{ 42 }}                       {{ 3.14 }}                {{ -10 }}
{{ true }}                     {{ false }}               {{ null }}
{{ [1, 2, 3] }}                {{ ['a', 'b', 'c'] }}
{{ {key: 'value'} }}           {{ {name: 'John', age: 30} }}

none is an alias of null; true, false, null and none also read in capitals (TRUE, FALSE, NULL, NONE), as in Twig. Printed, true gives 1 and false nothing.

Arrow Functions

Used with higher-order filters like map, filter, sort, reduce, and find:

{{ items|map(p => p.name) }}
{{ items|filter(p => p.active) }}
{{ items|find(p => p.id == 5) }}
{{ items|sort((a, b) => a.date <=> b.date) }}
{{ items|reduce((carry, item) => carry + item.price, 0) }}
{{ posts|filter(p => p.post_status == 'publish' and p.author.id == user.id) }}

As in Twig, map, filter and find pass the item's key as a second parameter, and reduce as a third:

{{ prices|map((price, name) => name ~ ': ' ~ price)|join(', ') }}
{{ prices|reduce((carry, price, name) => carry ~ name ~ ' ', '') }}

Named Arguments

As in Twig, an argument can be given by its name instead of its position. The arguments before it can then be left out, and keep their default:

{{ post.timestamp|date(timezone: 'Europe/Paris') }} <!-- Site date format, Paris time -->
{{ items|join(', ', and: ' and ') }}
{{ post.content|excerpt(num_words: 20) }}
{{ post.meta(field_name: 'subtitle') }}

Positional arguments come first, named ones after. The names are those of Twig and Timber, listed on each filter, function and field page; name = value works too, as in Twig. A name the filter does not have is ignored. An options object, such as post.excerpt({words: 25}), stays one argument: its keys are not argument names.

Escaping & Output

All output is automatically escaped — you never need to think about it. UnBlock combines two layers of protection:

• Field-aware: each field knows its type. Text fields use esc_html, URL fields like post.link use esc_url, and HTML fields like post.content are already processed by WordPress.
• Context-aware: URL attributes like href and src are escaped with esc_url, regardless of the field used. The attributes you set on a block are escaped with esc_attr.

{{ post.title }}                <!-- esc_html -->
{{ post.link }}                 <!-- esc_url everywhere -->
{{ post.content }}              <!-- Pre-processed HTML, safe to output -->
{{ '<b>Sale</b>' }}             <!-- Prints the tags as text -->

HTML written inside an expression, even in a string, is escaped and prints as text. Put the markup in your blocks and the data in the expression.

A list prints nothing: turn it into text first, for example with join. A block attribute whose whole value is one expression is removed when the expression gives null.

Comments are not rendered in the output:

{# This is a comment #}

Error Handling

Missing properties return an empty string — no errors. Properties are safely navigated even through null:

{{ post.nonexistent }}         <!-- Returns '' -->
{{ post.author.name }}         <!-- Safe even if author is null -->

An expression holds on one line and up to 500 characters. A longer one, or one with a syntax error, prints nothing.

Common mistake

Watch operator precedence when combining filters with fallback operators. {{ value ?? 'default'|upper }} applies upper to 'default' only — not to the whole result. Use parentheses: {{ (value ?? 'default')|upper }}.

Reserved Keywords

Cannot be used as variable names: true, false, null, none and the same in capitals, and, or, xor, not, in, is.

A variable named like a provider, such as post or site, hides that provider. Inside a loop, the loop's names and loop hide a variable of the same name. See Variables.

Next steps

• Your First Expression — learn the basics step by step
• Providers — all available data fields
• Filters — transform and format data
• Functions — built-in utility and WordPress functions
• Common Patterns — ready-to-use template examples