The by attribute specifies a relative offset value for an attribute that will be modified during an animation.

The starting value for the attribute is either indicated by specifying it as value for the attribute given in the attributeName or the from attribute.

Four elements are using this attribute: <animate><animateColor><animateMotion>, and <animateTransform>

<svg viewBox="0 0 200 200" xmlns="">
  <rect x="10" y="10" width="100" height="100">
    <animate attributeName="width" fill="freeze" by="50" dur="3s"/>

Usage notes

Value See below
Default value None
Animatable No

The exact value type for this attribute depends on the value of the attribute that will be animated.

When a list of values is defined via the values attribute, the by attribute is ignored.