function getAttr(/* tweenProp, */_, value) {
  const attrStartValues = {};
  Object.keys(value).forEach((attr) => {
    // get the value for 'fill-opacity' not fillOpacity
    // also 'width' not the internal 'width_px'
    const attribute = replaceUppercase(attr).replace(/_+[a-z]+/, '');
    const currentValue = this.element.getAttribute(attribute);
    attrStartValues[attribute] = svgColors.includes(attribute)
      ? (currentValue || 'rgba(0,0,0,0)')
      : (currentValue || (/opacity/i.test(attr) ? 1 : 0));
  });

  return attrStartValues;
}
Returns the current attribute value.
@param {string} _ the property name
@param {string} value the property value
@returns {{[x:string]: string}} attribute value