Haven’t you ever wondered why for some results, the summary does not contain any highlighted word?
Although the found document file does contain the searched word.
After having spent sometime, I think I found the explanation.
Basically, it is explained at http://goo.gl/RiSFBx.
In short, SharePoint keeps only 10,000 characters for each indexed file for the summary, and highlights the searched word only if it appears in the saved text.
