# Element metadata (sub-properties)

> Read an element's live measurements, like width, height, and position, to drive other elements.

Source: https://bluepic.io/help/expressions-and-logic/element-metadata-subproperties  
Language: en  
Category: expressions-and-logic  
Last updated: 2026-06-16

Every element exposes its live measurements, so one element can position or size itself relative to another. You read them as `element.property`, using the element's name and a dot.

The measurements you can read:

- **`width`**, **`height`**: the element's size.
- **`left`**, **`right`**, **`top`**, **`bottom`**: the position of each edge.
- **`x`**, **`y`**: the element's position.

For example, set a caption's Y position to `headline.bottom + 20` and the caption always sits 20 pixels below the headline, however long the headline grows. Change the headline and the caption follows automatically.

![](https://imagedelivery.net/mudX-CmAqIANL8bxoNCToA/8aba5b9e-8ba3-46c7-0f1b-c0be7f85ef00/max)

These measurements update live as content changes, which is what makes layouts that react to [dynamic text](https://bluepic.io/help/expressions-and-logic/guide-dynamic-text-layouts) possible. A [collection](https://bluepic.io/help/input-fields/input-fields-collection) also exposes `.length`, the number of items it currently holds.