Incorrect Key Name (customSpaceSize) in Theme Handbook > Spacing

[cawalle]

Issue Description

The documentation mistakenly refers to settings.spacing.customSpaceSize instead of the correct key, settings.spacing.customSpacingSize.

URL of the Page with the Issue

https://developer.wordpress.org/themes/global-settings-and-styles/settings/spacing/#defining-allowed-spacing-units

Section of Page with the Issue

The issue appears in the first paragraph of the "Defining allowed spacing units" section (linked above).

Why is this a Problem?

The incorrect key (customSpaceSize) prevents the feature from working as expected, potentially confusing theme developers who jump directly to this part of the documentation.

Suggested Fix

Replace settings.spacing.customSpaceSize with settings.spacing.customSpacingSize to reflect the correct key name.

[github-actions]

Heads up @WordPress/docs-issues-coordinators, we have a new issue open. Time to use 'em labels.