this property indicates the largest size in pixels the font is allowed to be. It defaults to 1000 pixels and much be set larger than or equal to the UITextSizeConstraint|UITextSizeConstraint's UITextSizeConstraint/MinTextSize|MinTextSize property.

If the affected GuiObject has its TextLabel/TextScaled|TextScaled property set to true the text size constrained by this property will scale dynamically with the container’s size. It will scale upwards with the GuiObject’s size until the max size is reached, at which point it will stay constant if the UI element continues to grow.