Manipulate RichText content

Hello everyone,

We are currently building a solution. Where we try to only pull the PlainText from a RichText component. Currently we got in our research two solutions proposed: 

1. Regex solution, which is prone to errors as we need to cather for various cases and exceptions
2. RichTextBox() functionality, that seems to do what we want as standard (see below) that but that throws an error

Seems this function is not used/available anymore in v8. Does anybody knows if it's possible to use this still in v8 via some additional set up in the app ? Or if we would have a corresponding similar rule in v8 environement ? Alternatively, would you have any suggestions as to how easily manipulate and extract plain text out of rich text object's code ?

Thank you in advance for your help!