Guidelines are a feature in DISE Composer providing control over the layout of objects. They are horizontal or vertical lines that appear on top of any content and allow you to align objects to them.
Guidelines are scene-specific. They may be inserted on a scene by simply clicking and dragging from a ruler - drag from the vertical ruler for a vertical guideline and the horizontal ruler for a horizontal.
Once inserted, they can be moved around by dragging.
The guideline menu can be reached by clicking the small box where the rulers meet.
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If you have a guideline specified, clicking the various Align buttons will align the object to it. You will be able to center an object in the area between guidelines or between guideline and screen border, or if you Align to full page, the area will be filled.