Content class property could be used for restricting the results’ type of indexing.

Here are some of the values, in case i forgot them some day :)

"STS_Web": // Site

"STS_List_850": // Page Library

"STS_ListItem_850": // Page

"STS_List_DocumentLibrary": // Document Library

"STS_ListItem_DocumentLibrary": // Document Library Items

"STS_List_GenericList": // Custom List

"STS_ListItem_GenericList": // Custom List Item

"STS_List_Links": // Links List

"STS_ListItem_Links": // Links List Item

"STS_List_Tasks": // Tasks List

"STS_ListItem_Tasks": // Tasks List Item

"STS_List_Events": // Events List

"STS_ListItem_Events": // Events List Item

"STS_List_Announcements": // Announcements List

"STS_ListItem_Announcements": // Announcements List Item

"STS_List_Contacts": // Contacts List

"STS_ListItem_Contacts": // Contacts List Item

"STS_List_DiscussionBoard": // Discussion List

"STS_ListItem_DiscussionBoard": // Discussion List Item

"STS_List_IssueTracking": // Issue Tracking List

"STS_ListItem_IssueTracking": // Issue Tracking List Item

"STS_List_GanttTasks": // Project Tasks List

"STS_ListItem_GanttTasks": // Project Tasks List Item

"STS_List_Survey": // Survey List

"STS_ListItem_Survey": // Survey List Item

"STS_List_PictureLibrary": // Picture Library

"STS_ListItem_PictureLibrary": // Picture Library Item

"STS_List_WebPageLibrary": // Web Page Library

"STS_ListItem_WebPageLibrary": // Web Page Library Item

"STS_List_XMLForm": // Form Library

"STS_ListItem_XMLForm": // Form Library Item