Block indentation

The block indentation feature lets you set indentation for text blocks such as paragraphs, headings, or lists. This way you can visually distinguish parts of your content.

Use the indent or outdent toolbar buttons in the editor below to change the indentation level. Try this on different elements: paragraphs, headings, and list items.

After installing the editor, add the feature to your plugin list and toolbar configuration:

import { ClassicEditor, Indent, IndentBlock } from 'ckeditor5';

ClassicEditor
	.create( document.querySelector( '#editor' ), {
		licenseKey: '<YOUR_LICENSE_KEY>', // Or 'GPL'.
		plugins: [ Indent, IndentBlock, /* ... */ ],
		toolbar: [ 'outdent', 'indent', /* ... */ ]
		indentBlock: {
			// Configuration.
		}
	} )
	.then( /* ... */ )
	.catch( /* ... */ );

const { ClassicEditor, Indent, IndentBlock } = CKEDITOR;

ClassicEditor
	.create( document.querySelector( '#editor' ), {
		licenseKey: '<YOUR_LICENSE_KEY>',
		plugins: [ Indent, IndentBlock, /* ... */ ],
		toolbar: [ 'outdent', 'indent', /* ... */ ]
		indentBlock: {
			// Configuration.
		}
	} )
	.then( /* ... */ )
	.catch( /* ... */ );

This feature offers a few configuration options that can be used to adjust the text block indentation behavior. It is implemented by three plugins: Indent, IndentBlock and List.

List block indentation uses the same configuration as block indentation for paragraphs and headings. The default indentation step is 40px. You can change it through the indentBlock configuration option, including switching to CSS classes.

By default, the block indentation feature increases or decreases the current indentation by the given offset, using the given unit.

The rich-text editor from the demo section above uses the default configuration, which defines a 40px indentation step.

You can change that value to, for example, 1em:

ClassicEditor
    .create( document.querySelector( '#editor' ), {
        // ... Other configuration options ...
        indentBlock: {
            offset: 1,
            unit: 'em'
        }
    } )
    .then( /* ... */ )
    .catch( /* ... */ );

If you want more semantics in your content, use CSS classes instead of fixed indentation units. You can then adjust the levels in the style sheets of your application whenever you want.

Here is how you can configure the block indentation feature to set indentation by applying one of the defined CSS classes:

ClassicEditor
    .create( document.querySelector( '#editor' ), {
        // ... Other configuration options ...
        indentBlock: {
            classes: [
                'custom-block-indent-a', // First step - smallest indentation.
                'custom-block-indent-b',
                'custom-block-indent-c'  // Last step - biggest indentation.
            ]
        }
    } )
    .then( /* ... */ )
    .catch( /* ... */ );

Using classes instead of fixed units (px or em) has another advantage – you retain control over what indentation levels are used in the documents. For instance, you can limit indentation to 2 or 3 different levels and there is no way the users can go beyond that. In the example above, the .custom-block-indent-c class level is the maximum allowed indentation value. This should help keep your content clean and predictable.

In this configuration, the WYSIWYG editor will restrict indentation levels to the set of provided classes. The class with the last index in the array has the biggest indentation.

In the demo below the CSS classes are defined as follows:

.custom-block-indent-a {
    margin-left: 10%;
}

.custom-block-indent-b {
    margin-left: 20%;
}

.custom-block-indent-c {
    margin-left: 30%;
}

Besides controlling text block indentation, the same set of buttons (outdent, indent) allows for indenting list items (nesting them).

This mechanism is completely transparent to the user. From the code perspective, the buttons are implemented by the Indent plugin, but neither these buttons nor the respective commands implement any functionality by default.

The target behavior comes from two other plugins:

• IndentBlock – The indent block feature controls the indentation of elements such as paragraphs and headings.
• List – The list feature implements the indentation (nesting) of lists.

This means that if you want to allow indenting lists only, you can do that by loading the Indent and List plugins only. If you want the full behavior – nesting list items, block indentation of paragraphs and headings, and visual block indentation of lists – you need to load all three plugins: Indent, IndentBlock, and List.

When all three plugins are loaded, the editor also supports applying visual block indentation to list containers (<ol>, <ul>) and list items (<li>). This works the same way as block indentation for paragraphs and headings – it adds a margin-left style (or a CSS class, depending on the configuration) to the list elements. The editor understands margin-left styles on all these elements during data loading, across all list types (numbered, bulleted, to-do, multi-level) and at all nesting levels. Negative indentation values (such as -50px) are also accepted during data loading.

Only the topmost list in the content can be indented or outdented. The selection must be at the start of the list (collapsed or non-collapsed). Use one of the following methods:

• Press Tab to indent or Shift+Tab to outdent the list. The indentation changes in steps (by default, 40px).
• Use the indent and outdent toolbar buttons. The indentation also changes in steps.

It is not possible to outdent a list below 0 as negative values cannot be set through the editor UI. If a list with a negative indentation value was loaded into the editor, indenting it resets the value to 0 in a single step.

You can also remove the list indentation using the remove format feature, which removes the indentation attribute in one step.

List items cannot be indented through the editor UI. However, indentation values on <li> elements are recognized during data loading.

A list item’s indentation can only be reset in a single step by:

• Using the indent button (if the value is negative) or the outdent button (if the value is positive).
• Using the remove format feature.

The selection must be set inside a list item (or span multiple list items) for these actions to work.

Here are some CKEditor 5 features that may help structure your content better:

• Block quote – Include block quotations or pull quotes in your rich-text content.
• Headings – Divide your content into sections.
• Code block – Insert longer, multiline code listings.
• Text alignment – Because it does matter whether the content is left, right, centered, or justified.

The Indent plugin registers the following components:

• The 'indent' command.

  This command does not implement any indentation behavior by itself. It executes either indentBlock (described below) or indentList, depending on which of these commands is enabled.

  Read more in the Indenting lists section above.

• The 'outdent' command.

  This command does not implement any indentation behavior by itself. It executes either outdentBlock (described below) or outdentList, depending on which of these commands is enabled.

  Read more in the Indenting lists section above.

The IndentBlock plugin registers the following components:

• The 'indentBlock' command.

  You can increase the indentation of the text block that contains the selection by:

  editor.execute( 'indentBlock' );
  

  Copy code

• The 'outdentBlock' command.

  You can decrease the indentation of the text block that contains the selection by:

  editor.execute( 'outdentBlock' );
  

  Copy code

The source code of the feature is available on GitHub at https://github.com/ckeditor/ckeditor5/tree/master/packages/ckeditor5-font.