diff --git a/docs/docs/core/custom_function.mdx b/docs/docs/core/custom_function.mdx
index 841ac2fd0..1f60ed245 100644
--- a/docs/docs/core/custom_function.mdx
+++ b/docs/docs/core/custom_function.mdx
@@ -148,6 +148,17 @@ Custom functions take the following additional parameters:
     When the version is changed, the function will be re-executed even if cache is enabled.
     It's required to be set if `cache` is `True`.
 
+*   `arg_relationship: tuple[ArgRelationship, str]`: It specifies the relationship between an input argument and the output,
+    e.g. `(ArgRelationship.CHUNKS_BASE_TEXT, "content")` means the output is chunks for the text represented by the
+    input argument with name `content`.
+    This provides metadata for tools, e.g. CocoInsight.
+    Currently the following attributes are supported:
+
+    *   `ArgRelationship.CHUNKS_BASE_TEXT`:
+        The output is chunks for the text represented by the input argument. In this case, the output is expected to be a *Table*, whose each row represents a text chunk, and the first column has type *Range*, representing the range of the text chunk.
+    *   `ArgRelationship.EMBEDDING_ORIGIN_TEXT`: The output is embedding vector for the text represented by the input argument. The output is expected to be a *Vector*.
+    *   `ArgRelationship.RECTS_BASE_IMAGE`: The output is rectangles for the image represented by the input argument. The output is expected to be a *Table*, whose each row represents a rectangle, and the first column has type *Struct*, with fields `min_x`, `min_y`, `max_x`, `max_y` to represent the coordinates of the rectangle.
+
 For example:
 
 <Tabs>
diff --git a/python/cocoindex/functions.py b/python/cocoindex/functions.py
index 3b88d26aa..9b0763c13 100644
--- a/python/cocoindex/functions.py
+++ b/python/cocoindex/functions.py
@@ -70,7 +70,7 @@ class SentenceTransformerEmbed(op.FunctionSpec):
     gpu=True,
     cache=True,
     behavior_version=1,
-    arg_relationship=(op.ArgRelationship.VECTOR_ORIGIN_TEXT, "text"),
+    arg_relationship=(op.ArgRelationship.EMBEDDING_ORIGIN_TEXT, "text"),
 )
 class SentenceTransformerEmbedExecutor:
     """Executor for SentenceTransformerEmbed."""
diff --git a/python/cocoindex/op.py b/python/cocoindex/op.py
index a256027cb..d4bc51e08 100644
--- a/python/cocoindex/op.py
+++ b/python/cocoindex/op.py
@@ -91,7 +91,7 @@ def __call__(
 class ArgRelationship(Enum):
     """Specifies the relationship between an input argument and the output."""
 
-    VECTOR_ORIGIN_TEXT = _COCOINDEX_ATTR_PREFIX + "vector_origin_text"
+    EMBEDDING_ORIGIN_TEXT = _COCOINDEX_ATTR_PREFIX + "embedding_origin_text"
     CHUNKS_BASE_TEXT = _COCOINDEX_ATTR_PREFIX + "chunk_base_text"
     RECTS_BASE_IMAGE = _COCOINDEX_ATTR_PREFIX + "rects_base_image"
 
diff --git a/src/base/field_attrs.rs b/src/base/field_attrs.rs
index 1cc80fee8..b4b1a8236 100644
--- a/src/base/field_attrs.rs
+++ b/src/base/field_attrs.rs
@@ -15,4 +15,4 @@ pub static CONTENT_MIME_TYPE: &str = concatcp!(COCOINDEX_PREFIX, "content_mime_t
 pub static CHUNK_BASE_TEXT: &str = concatcp!(COCOINDEX_PREFIX, "chunk_base_text");
 
 /// Base text for an embedding vector.
-pub static _VECTOR_ORIGIN_TEXT: &str = concatcp!(COCOINDEX_PREFIX, "vector_origin_text");
+pub static _EMBEDDING_ORIGIN_TEXT: &str = concatcp!(COCOINDEX_PREFIX, "embedding_origin_text");