Put the function of building index to the right-click context of folders, and give users an option to build the search index on some special folder they have selected and not all contents on computer. I think to do so will improve the building speed and retrieval accuracy.
Give the context label name as “Anytxt Here” or others similar. When the user only want to search some keyword in only one folder and its subfolder, he could use this function easily instead of choosing the exact folder on the search window complexily. And then, Anytxt will return the search results only about the special folder among all the large amount of index contents about the whole computer, OR temporary execute the building index functions on this special folder and its subfolder, and return the results. No matter which method you use, Anytxt can improve search speed and accuracy.