diff --git a/src/api/annotation.rs b/src/api/annotation.rs
index 0e6178f..942b401 100644
--- a/src/api/annotation.rs
+++ b/src/api/annotation.rs
@@ -166,6 +166,7 @@ impl<'store> ResultItem<'store, Annotation> {
 
     /// Returns the (single!) resource the annotation points to. Only works if this annotation targets using a [`Selector::TextSelector`],
     /// [`Selector::ResourceSelector`] or [`Selector::AnnotationSelector`], and not for complex selectors.
+    /// Use [`Self::resources()`] if want to iterate over all resources instead.
     /// AnnotationSelectors are followed recursively if needed.
     pub fn resource(&self) -> Option<ResultItem<'store, TextResource>> {
         match self.as_ref().target() {
@@ -629,7 +630,7 @@ impl<'store> AnnotationsIter<'store> {
     pub fn filter_annotations(mut self, annotations: AnnotationsIter<'store>) -> Self {
         if self.iter.is_some() {
             if annotations.iter.is_some() {
-                self.iter = Some(self.iter.unwrap().merge(annotations.iter.unwrap()));
+                self.iter = Some(self.iter.unwrap().intersection(annotations.iter.unwrap()));
             } else {
                 //invalidate the iterator, there will be no results
                 self.abort();
@@ -817,10 +818,11 @@ impl<'store> AnnotationsIter<'store> {
     }
 
     /// Produces the union between two annotation iterators
-    /// Any constraints on either iterator remain valid!
-    pub fn extend(mut self, other: AnnotationsIter<'store>) -> AnnotationsIter<'store> {
+    /// Any filters on either iterator remain valid!
+    pub fn union(mut self, other: AnnotationsIter<'store>) -> AnnotationsIter<'store> {
         if self.iter.is_some() && other.iter.is_some() {
-            self.iter = Some(self.iter.unwrap().extend(other.iter.unwrap()));
+            self.filters.extend(other.filters.into_iter());
+            self.iter = Some(self.iter.unwrap().union(other.iter.unwrap()));
         } else if self.iter.is_none() {
             return other;
         }
@@ -828,10 +830,11 @@ impl<'store> AnnotationsIter<'store> {
     }
 
     /// Produces the intersection between two annotation iterators
-    /// Any constraints on either iterator remain valid!
-    pub fn merge(mut self, other: AnnotationsIter<'store>) -> AnnotationsIter<'store> {
+    /// Any filters on either iterator remain valid!
+    pub fn intersection(mut self, other: AnnotationsIter<'store>) -> AnnotationsIter<'store> {
         if self.iter.is_some() && other.iter.is_some() {
-            self.iter = Some(self.iter.unwrap().extend(other.iter.unwrap()));
+            self.filters.extend(other.filters.into_iter());
+            self.iter = Some(self.iter.unwrap().intersection(other.iter.unwrap()));
         } else if self.iter.is_none() {
             return other;
         }
diff --git a/src/api/annotationdata.rs b/src/api/annotationdata.rs
index d4c4e46..940160b 100644
--- a/src/api/annotationdata.rs
+++ b/src/api/annotationdata.rs
@@ -298,7 +298,7 @@ impl<'store> DataIter<'store> {
     ///
     /// You can cast any existing iterator that produces [`ResultItem<AnnotationData>`] to a [`DataIter`] using [`DataIter::from_iter()`].
     pub fn filter_data(self, data: DataIter<'store>) -> Self {
-        self.merge(data)
+        self.intersection(data)
     }
 
     /// Find and filter data. Returns an iterator over the data.
@@ -447,10 +447,11 @@ impl<'store> DataIter<'store> {
     }
 
     /// Produces the union between two data iterators
-    /// Any constraints on either iterator remain valid!
-    pub fn extend(mut self, other: DataIter<'store>) -> DataIter<'store> {
+    /// Any filters on either iterator remain valid!
+    pub fn union(mut self, other: DataIter<'store>) -> DataIter<'store> {
         if self.iter.is_some() && other.iter.is_some() {
-            self.iter = Some(self.iter.unwrap().extend(other.iter.unwrap()));
+            self.filters.extend(other.filters.into_iter());
+            self.iter = Some(self.iter.unwrap().union(other.iter.unwrap()));
         } else if self.iter.is_none() {
             return other;
         }
@@ -458,10 +459,11 @@ impl<'store> DataIter<'store> {
     }
 
     /// Produces the intersection between two data iterators
-    /// Any constraints on either iterator remain valid!
-    pub fn merge(mut self, other: DataIter<'store>) -> DataIter<'store> {
+    /// Any filters on either iterator remain valid!
+    pub fn intersection(mut self, other: DataIter<'store>) -> DataIter<'store> {
         if self.iter.is_some() && other.iter.is_some() {
-            self.iter = Some(self.iter.unwrap().merge(other.iter.unwrap()));
+            self.filters.extend(other.filters.into_iter());
+            self.iter = Some(self.iter.unwrap().intersection(other.iter.unwrap()));
         } else if self.iter.is_none() {
             return other;
         }
diff --git a/src/api/resources.rs b/src/api/resources.rs
index eeb725e..f4092f6 100644
--- a/src/api/resources.rs
+++ b/src/api/resources.rs
@@ -62,7 +62,7 @@ impl<'store> ResultItem<'store, TextResource> {
     /// Use `annotations_as_metadata()` or `annotations_on_text()` instead if you want to differentiate the two.
     pub fn annotations(&self) -> AnnotationsIter<'store> {
         self.annotations_as_metadata()
-            .extend(self.annotations_on_text())
+            .union(self.annotations_on_text())
     }
 
     /// Returns an iterator over all text selections that are marked in this resource (i.e. there are one or more annotations on it).
@@ -306,6 +306,30 @@ impl<'store> ResourcesIter<'store> {
         self
     }
 
+    /// Produces the union between two resource iterators
+    /// Any filters on either iterator remain valid!
+    pub fn union(mut self, other: ResourcesIter<'store>) -> ResourcesIter<'store> {
+        if self.iter.is_some() && other.iter.is_some() {
+            self.filters.extend(other.filters.into_iter());
+            self.iter = Some(self.iter.unwrap().union(other.iter.unwrap()));
+        } else if self.iter.is_none() {
+            return other;
+        }
+        self
+    }
+
+    /// Produces the intersection between two resource iterators
+    /// Any filters on either iterator remain valid!
+    pub fn intersection(mut self, other: ResourcesIter<'store>) -> ResourcesIter<'store> {
+        if self.iter.is_some() && other.iter.is_some() {
+            self.filters.extend(other.filters.into_iter());
+            self.iter = Some(self.iter.unwrap().intersection(other.iter.unwrap()));
+        } else if self.iter.is_none() {
+            return other;
+        }
+        self
+    }
+
     /// Does this iterator return items in sorted order?
     pub fn returns_sorted(&self) -> bool {
         if let Some(iter) = self.iter.as_ref() {
diff --git a/src/lib.rs b/src/lib.rs
index ff38b18..6f2b5a9 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -267,7 +267,7 @@ where
 
     /// Merges another IntersectionIter into the current one. This effectively
     /// iterates over the intersection of both.
-    pub(crate) fn merge(mut self, other: IntersectionIter<'a, T>) -> Self {
+    pub(crate) fn intersection(mut self, other: IntersectionIter<'a, T>) -> Self {
         for source in other.sources {
             if source.array.is_some() {
                 self = self.with(source.array.unwrap(), source.sorted);
@@ -283,7 +283,7 @@ where
 
     /// Extends this iterator with another one. This is a *union* and not an *intersection*.
     /// However, all additional constraints on either iterator are preserved (and those are intersections).
-    pub(crate) fn extend(mut self, mut other: IntersectionIter<'a, T>) -> Self {
+    pub(crate) fn union(mut self, mut other: IntersectionIter<'a, T>) -> Self {
         //edge-cases first:
         if self.sources.is_empty() {
             return other;
@@ -557,21 +557,21 @@ mod test {
     }
 
     #[test]
-    fn test_intersectioniter_merge() {
+    fn test_intersectioniter_intersection() {
         let mut iter = IntersectionIter::new(Cow::Owned(vec![1, 2, 3, 4, 5]), true);
         iter = iter.with(Cow::Owned(vec![1, 3, 5]), true);
         let iter2 = IntersectionIter::new(Cow::Owned(vec![5, 6]), true);
-        iter = iter.merge(iter2);
+        iter = iter.intersection(iter2);
         iter = iter.with(Cow::Owned(vec![5]), true);
         let v: Vec<_> = iter.collect();
         assert_eq!(v, vec![5]);
     }
 
     #[test]
-    fn test_intersectioniter_extend() {
+    fn test_intersectioniter_union() {
         let mut iter = IntersectionIter::new(Cow::Owned(vec![1, 2, 3, 4, 5]), true);
         let iter2 = IntersectionIter::new(Cow::Owned(vec![6, 7]), true);
-        iter = iter.extend(iter2);
+        iter = iter.union(iter2);
         let v: Vec<_> = iter.collect();
         assert_eq!(v, vec![1, 2, 3, 4, 5, 6, 7]);
     }