docs: clarify YAML type expressions vs signature short names

site/docs/extensions/index.md

@@ -74,7 +74,7 @@ The resulting function signatures look like: `<function_name>:<short_arg_type0>_
     argument-signature = short-arg-type *("_" short-arg-type)
     ```
 
-Argument types (`short_arg_type`) are encoded using the Type Short Names given below.
+Argument types (`short_arg_type`) are encoded using the [Type Short Names](#type-short-names) given below.
 
 #### Variadic Functions
 
@@ -86,8 +86,13 @@ A function signature uniquely identifies a function implementation within a sing
 
 #### Type Short Names
 
-| Argument Type                   | Signature Name |
-|---------------------------------|----------------|
+!!! note "Type expressions vs. signature short names"
+    Type-valued fields in extension YAML use [type expressions](../types/type_parsing.md), such as `string`, `binary`, and `fixedbinary<16>`. Signature short names are only used when constructing function signatures, such as `concat:str` or `hash:vbin`.
+
+The first column lists the type expression used in extension YAML. The second column lists the corresponding short name used in function signatures.
+
+| YAML Type Expression            | Signature Short Name |
+|---------------------------------|----------------------|
 | Enumeration                     | req            |
 | i8                              | i8             |
 | i16                             | i16            |

site/docs/types/type_parsing.md

@@ -17,7 +17,7 @@ The components of this expression are:
 
 ### Grammars
 
-It is relatively easy in most languages to produce simple parser & emitters for the type syntax. To make that easier, Substrait also includes an [ANTLR grammar](https://github.com/substrait-io/substrait-cpp/blob/main/src/substrait/textplan/parser/grammar/SubstraitPlanParser.g4#L108) to ease consumption and production of types.  (The grammar also supports an entire language for representing plans as text.)
+It is relatively easy in most languages to produce simple parser & emitters for the type syntax. To make that easier, Substrait also includes an [ANTLR grammar](https://github.com/substrait-io/substrait/blob/main/grammar/SubstraitType.g4) to ease consumption and production of types.
 
 ### Structs & Named Structs
 

tests/README.md

@@ -213,7 +213,7 @@ Use short names listed in https://substrait.io/extensions/#function-signature-co
 - **str**: Variable-length string
 - **fchar**: Fixed-length string `fixedchar<N>`
 - **vchar**: Variable-length string `varchar<N>`
-- **vbin**: Fixed-length binary `fixedbinary<N>`
+- **vbin**: Variable-length binary `binary`
 - **date**: Date
 - **iyear**: Interval year
 - **iday**: Interval days `interval_day<P>`