According to the programmer:
Spotlight was introduced in Mac OS X Tiger. Spotlight can search the local hard drive and it is great! However, Spotlight only displays a list of the files that contain the query keyword. Users must open each file to see what it is and how the keyword is used in the file. That’s ridiculous and I think Apple should improve this bad user experience. That’s why I made this small software, SpotInside, which shows its contents just by clicking the result list and it highlights the keyword as well.
Here is the link: SpotInside