Query criteria as a tree
To HoudahSpot your query appears as a tree. In that tree the criteria are leaves strung together in groups. Groups are boolean operators that act as nodes in the tree.
ALL of the following are true
A branch of criteria combined in an "ALL group" can only be matched by files that match each and every immediate child of the operator. This is the most common situation.
ANY of the following are true
In order to match an "ANY group" a file needs match at least one of the immediate child branches or criteria.
NONE of the following are true
In order to match an "NONE group" a file may not match any of the immediate child branches or criteria.
Adding groups
Groups are created by option-clicking the "+" button at the far right of a criteria row.
A world of metadata attributes
Spotlight may index a myriad of file properties. The actual set of properties varies by file type and is the responsibility of the Spotlight importer used by the system to index the file. Spotlight importers are provided either by Apple or by application editors. They act in a way that is transparent to the user.
HoudahSpot may query all those attributes. While the default document is configured only for the most commonly used attributes you may add others to your liking.
To the left of each row in the criteria pane is the attribute pop-up. You may select attributes to query from this menu. At the bottom of this menu is a special item. The "Other..." item will open a list of attributes known to Spotlight. You may select the appropriate attribute from that list.
E.g. the "Content type" attribute allows you to find documents of a given type. Possible values for this type of criteria include com.microsoft.word.doc, com.microsoft.excel.xls and com.adobe.photoshop-image. This criteria is most easily configured by drag-and-dropping an existing file onto the criteria row.