If you are creating search scopes you have four options to configure your scope rule type:
1. Web Address
2. Property Query
3. Content Source
4. All Content

If you choose the option ‘Property Query’ you will be asked to select one of the property restrictions. Again you have four options to select from:
1. Author
2. Contentclass
3. Site
4. SiteName

Author, Site and SiteName will do just what the name tells you. Select content by author, select content by its site location or select content by the sitename.
For your convenience here are all values that you can specify with the ContentClass:
- Search Query: urn:content-class:SPSSearchQuery
- News Listing: urn:content-class:SPSListing:News
- People: urn:content-class:SPSPeople
- Category: urn:content-classes:SPSCategory
- Listing: urn:content-classes:SPSListing
- Person Listing: urn:content-classes:SPSPersonListing
- Text Listing: urn:content-classes:SPSTextListing
- Site Listing: urn:content-classes:SPSSiteListing
- Site Registry Listing: urn:content-classes:SPSSiteRegistry
- Site: STS_Web
- List: STS_List
- List Item: STS_ListItem
- Events: STS_List_Events
- Tasks: STS_List_Tasks
- Announcements: STS_List_Announcements
- Discussions: STS_List_DiscussionBoard
- Contacts: STS_List_Contacts
- Links: STS_List_Links
- Document Library: STS_List_DocumentLibrary
- Document Library Items: STS_ListItem_DocumentLibrary
- Picture Library: STS_List_PictureLibrary
- Picture Library Items: STS_ListItem_PictureLibrary
Ciao,
Niels