Not built-in, but here is one way to do it: http://world.episerver.com/blogs/Per-Magne-Skuseth/Dates/2016/1/episerver-find-index-blocks-in-xhtmlstring/
Thanks Per. I haven't had time to do it myself yet, so I think your blogpost will be a good guide. :)
if you have a block in a Xhtml-string, the content of the block is not included in the index of that page/property. Is there a built-in way to solve this (like IndexInContentAreas) or do I need to create my own solution?