What is it?
The Define Start and the Define End filters are filters used to tell a parser where to begin looking for text and where to end based on consistent keywords within a document.
How is it used?
Add Filter > Crop From Start & End > Define Start Position
The Define Start and End filters work by designating a keyword as a place to begin looking for your data. A common use case when grabbing an Invoice Number would be to use the text in your invoice field as a starting point.