> ## Documentation Index > Fetch the complete documentation index at: /llms.txt > Use this file to discover all available pages before exploring further. # Line Swap > A masked full-line beat replacement: line A holds center then exits up through an overflow-hidden mask as line B enters bottom-up on the same beat, with an optional accent underline drawing beneath one word of line B. # Line Swap A masked full-line beat replacement: line A holds center then exits up through an overflow-hidden mask as line B enters bottom-up on the same beat, with an optional accent underline drawing beneath one word of line B. **Line Swap** ```html line-swap.html Line Swap ``` Copy npx hyperframes add line-swap to the clipboard That writes one file: `compositions/components/line-swap.html`. ## Paste it into your composition Open `compositions/components/line-swap.html` and copy what is inside into your own composition. A component has no size or duration of its own. It takes both from the composition you paste it into. ## Variables Every one of these has a default, so the piece works untouched. Set the ones you want to change on the element: | Variable | Default | Accepts | What it does | | - | - | - | - | | `line_a` | `Everyone promised you AI.` | string | First line; holds center inside the mask, then exits up on the swap beat. | | `line_b` | `Almost nobody promised you control.` | string | Replacement line; enters bottom-up on the swap beat and holds. | | `swap_at` | `1.5` | number | Second (from mount start) of the beat replacement. Clamped so the swap and underline complete before any exit. | | `underline_word` | `control` | string | First case-insensitive substring match in line B gets the accent underline after landing. Empty disables it. | | `accent` | `green` | `green`, `blue`, `violet` | Underline color from the contract token map. | | `exit` | `none` | `none`, `fade`, `up` | Optional departure. Default none: the landed line holds until the frame cuts. | Set them with `data-variable-values` on the element that mounts it. These are the defaults, so this behaves exactly like the preview above until you change one: ```html wrap
``` {/* hf:generated-footer */} Tagged `motion-primitive` `text-effects` `swap` `beat` `deterministic`. ## Related topics * [Browse the complete Catalog](/catalog.md) * [Add assets and Catalog items in the browser editor](/studio/assets-and-blocks.md) * [Put blocks together into one video](/concepts/compositions.md)