If you are searching for text in tags, you can use the extremely versatile app Integrated Search Views (which permits an enormous variety of filtering and handling options). You don’t need to do so, however, because the Advanced Display Filter (new in Studio 2017) will look for the text you are searching for also in tags (although it doesn’t tell you that explicitly).
However, there is a downside to this: As yet, you cannot turn this function off, which means that if you are searching for an expression in the text which happens to contain also tags (for instance formatting tags), then this filter will not find the expression because it will see the tags (which you did not include in your search string) as well.
But there is a simple remedy: the “basic” Display Filter does not work in this way. So if you don’t need any of the more advanced functions in the Advanced Display Filter but only are looking for plain text – use the basic filter function and you’ll be fine.
You can read more about this in detail here (if you have an SDL account).