Function and usage of make_before_block_visitor() in wordpress


Answers ( 1 )


    The make_before_block_visitor() function in WordPress is a specialized function primarily intended for internal use. Its primary purpose is to inject specific attributes and prepend certain blocks before a given block during the block rendering process. Here's a detailed explanation of the function and a sample usage:

    Function Signature

    make_before_block_visitor( array $hooked_blocks, WP_Block_Template|array $context ): callable


    • Functionality: The function make_before_block_visitor() generates a callable function that can be used to modify block rendering. This callable is particularly designed to inject a 'theme' attribute into Template Part blocks and to prepend markup for blocks that are hooked before a specific block.
    • Usage Context: This function is primarily used in the context of traverse_and_serialize_block(s), where it serves as the $pre_callback argument. It manipulates block rendering in the context of a block template or a pattern.


    1. $hooked_blocks (array, required):

      • Description: An array of blocks that are hooked to another given block.
      • Purpose: This array dictates which blocks should be prepended to the specified block during rendering.
    2. $context (WP_Block_Template|array, required):

      • Description: This can either be a block template, a template part, or a pattern.
      • Purpose: Provides the context in which the blocks belong, guiding how the blocks should be manipulated.


    • Type: callable
    • Description: The returned value is a function that, when called, returns the serialized markup for the given block. This includes the markup for any hooked blocks that are supposed to appear before it.

    Sample Usage

    Here's an example of how make_before_block_visitor() might be used in a WordPress theme or plugin:

    // Define the blocks that need to be hooked
    $hooked_blocks = [
        // ... (blocks configuration)
    // Define the context, such as a specific block template
    $context = /* WP_Block_Template or array representing the context */;
    // Create the pre_callback function using make_before_block_visitor
    $pre_callback = make_before_block_visitor($hooked_blocks, $context);
    // Use the pre_callback in traverse_and_serialize_blocks
    $rendered_blocks = traverse_and_serialize_blocks( $blocks, $pre_callback );

    Important Notes

    • Internal Use: This function is meant for internal use within WordPress core. It’s designed for developers who are familiar with WordPress's inner workings, particularly in block rendering.
    • Complexity: Given its nature, the function might be complex and not suitable for general WordPress theme or plugin development. It’s primarily aimed at advanced users and core developers.

    This explanation and sample usage should provide a clear understanding of the make_before_block_visitor() function in WordPress, including its purpose, parameters, and how it might be used in a practical scenario.

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