Move expressions to types and correct links

_data/link.yml

@@ -218,9 +218,11 @@ VgEventStream:
 SelectionResolution:
   link: "selection.html#resolve"
 
-# Others
+# Types
 DateTime:
   link: "types.html#datetime"
+
+# Others
 HorizontalAlign:
   name: String
 VerticalAlign:

build/vega-lite-schema.json

@@ -813,7 +813,7 @@
           "type": "string"
         },
         "calculate": {
-          "description": "A string containing a Vega Expression. Use the variable `datum` to refer to the current data object.",
+          "description": "A [expression](types.html#expression) string. Use the variable `datum` to refer to the current data object.",
           "type": "string"
         }
       },
@@ -2078,7 +2078,7 @@
       "properties": {
         "filter": {
           "$ref": "#/definitions/LogicalOperand<Predicate>",
-          "description": "The `filter` property must be one of the predicate definitions:\n(1) a [Vega Expression](filter.html#expression) string,\nwhere `datum` can be used to refer to the current data object;\n(2) one of the field predicates: [equal predicate](filter.html#equal-predicate);\n[range precidate](filter.html#range-predicate), [one-of predicate](filter.html#one-of-predicate);\n(3) a [selection predicate](filter.html#selection-predicate);\nor (4) a logical operand that combines (1), (2), or (3)."
+          "description": "The `filter` property must be one of the predicate definitions:\n(1) an [expression](types.html#expression) string,\nwhere `datum` can be used to refer to the current data object;\n(2) one of the field predicates: [equal predicate](filter.html#equal-predicate);\n[range precidate](filter.html#range-predicate), [one-of predicate](filter.html#one-of-predicate);\n(3) a [selection predicate](filter.html#selection-predicate);\nor (4) a logical operand that combines (1), (2), or (3)."
         }
       },
       "required": [

site/docs/transform/calculate.md

@@ -5,7 +5,7 @@ title: Calculate Transform
 permalink: /docs/calculate.html
 ---
 
-The formula transform extends data objects with new fields (columns) according to a calculation formula.
+The formula transform extends data objects with new fields (columns) according to an [expression](types.html#expression).
 
 {: .suppress-error}
 ```json
@@ -23,6 +23,6 @@ The formula transform extends data objects with new fields (columns) according t
 
 ## Example
 
-This example use `calculate` to derive a new field, then `filter` data based on the new field.
+This example uses `calculate` to derive a new field, and  then `filter`s the data based on the new field.
 
 <span class="vl-example" data-name="bar_filter_calc"></span>

site/docs/transform/filter.md

@@ -27,7 +27,7 @@ Vega-Lite filter transforms must have the `filter` property describing the predi
 {:#expression}
 ## Filter Expression
 
-For a [Vega Expression](https://vega.github.io/vega/docs/expressions/) string, each datum object can be referred using bound variable `datum`. For example, setting `filter` to `"datum.b2 > 60"` would make the output data includes only items that have values in the field `b2` over 60.
+For an [expression](types.html#expression) string, each datum object can be referred using bound variable `datum`. For example, setting `filter` to `"datum.b2 > 60"` would make the output data includes only items that have values in the field `b2` over 60.
 
 
 ## Field Predicate

site/docs/types.md

@@ -5,81 +5,82 @@ title: Parameter Types
 permalink: /docs/types.html
 ---
 
-Reference documentation for common parameter **types** expected by Vega specification properties.
+Reference documentation for common parameter **types** expected by Vega-Lite specification properties.
 
 {:#reference}
 ## Parameter Type Reference
 
-- [Any](#Any)
-- [Array](#Array)
-- [Boolean](#Boolean)
-- [Color](#Color)
-- [Number](#Number)
-- [Object](#Object)
-- [String](#String)
-- [URL](#URL)
-- [DateTime](#DateTime)
-- [Field](#Field)
-- [Signal](#Signal)
-- [Compare](#Compare)
-- [Expr](#Expr)
-- [Value](#Value)
-- [ColorValue](#ColorValue)
-- [FieldValue](#FieldValue)
+- [Any](#any)
+- [Array](#array)
+- [Boolean](#boolean)
+- [Color](#color)
+- [DateTime](#datetime)
+- [Expressions](#expression)
+- [Number](#number)
+- [Object](#object)
+- [String](#string)
+- [URL](#url)
 {: .column-list }
 
 ## Literal Values
 
-<a name="*"></a><a name="Any" href="#Any">#</a>
+<a name="*"></a><a name="any" href="#any">#</a>
 **Any** or **\***
 
 Accepts any literal value, including a string, number, boolean, or `null`.
 
-<br/><a name="Array" href="#Array">#</a>
+<br/><a name="array" href="#array">#</a>
 **Array** or **Type[]**
 
-Accepts array values. For example: `[]`, `[1, 2, 3]`, `["foo", "bar"]`. If individual array items must adhere to a specific type, bracket notation &ndash; such as Number[] or String[] &ndash; is used to indicate the item type.
+Accepts array values. For example: `[]`, `[1, 2, 3]`, `["foo", "bar"]`. If individual array items must adhere to a specific type, bracket notation &ndash; such as `Number[]` or `String[]` &ndash; is used to indicate the item type.
 
 In most cases, arrays may also have [signal references](#Signal) as items. For example: `[{"signal": "width"}, {"signal": "height"}]`.
 
-<br/><a name="Boolean" href="#Boolean">#</a>
+<br/><a name="boolean" href="#boolean">#</a>
 **Boolean**
 
 Accepts boolean values. For example: `true`, `false`.
 
-<br/><a name="Color" href="#Color">#</a>
+<br/><a name="color" href="#color">#</a>
 **Color**
 
 Accepts a valid CSS color string. For example: `#f304d3`, `#ccc`, `rgb(253, 12, 134)`, `steelblue`.
 
-<br/><a name="Number" href="#Number">#</a>
+<br/><a name="datetime" href="#datetime">#</a>
+**DateTime**
+
+A DateTime object (in [filter transform](filter.html), [scale domain](scale.html#domain), and [axis](axis.html#ticks)/[legend](legend.html#properties) values) must have at least one of the following properties:
+
+{% include table.html props="year,quarter,month,date,day,hours,minutes,seconds,milliseconds" source="DateTime" %}
+
+For example `{"year": 2006, "month": "jan", "date": 1}` represents _Jan 1, 2006_.
+
+<br/><a name="expression" href="#expression">#</a>
+**Expression**
+
+To enable custom calculations, Vega-Lite uses Vega's expression language for writing basic formulas. Each datum object can be referred using bound variable `datum`.
+
+Please read the [Vega documentation for expressions](https://vega.github.io/vega/docs/expressions/) for details.
+
+
+<br/><a name="number" href="#number">#</a>
 **Number**
 
 Accepts number values. For example: `1`, `3.14`, `1e5`.
 
-<br/><a name="Object" href="#Object">#</a>
+<br/><a name="object" href="#object">#</a>
 **Object**
 
 Accepts object literals. For example: `{"left":5, "right":30, "top":5, "bottom":50}`. The valid object property names and types will vary across parameters; read the individual parameter descriptions for more information.
 
 
-<br/><a name="String" href="#String">#</a>
+<br/><a name="string" href="#string">#</a>
 **String**
 
 Accepts string values. For example: `"bold"`, `"step-before"`, `""`.
 
 
-<br/><a name="URL" href="#URL">#</a>
+<br/><a name="url" href="#url">#</a>
 **URL**
 
 Accepts a valid URL string linking to external site or resource. For example: `"data/stocks.csv"`, `"images/logo.png"`, `"https://vega.github.io/"`.
-
-
-<br/><a name="datetime" href="#datetime">#</a>
-**DateTime**
-
-A DateTime object (in [filter transform](filter.html), [scale domain](scale.html#domain), and [axis](axis.html#ticks)/[legend](legend.html#properties) values) must have at least one of the following properties:
-
-{% include table.html props="year,quarter,month,date,day,hours,minutes,seconds,milliseconds" source="DateTime" %}
-
-For example `{"year": 2006, "month": "jan", "date": 1}` represents _Jan 1, 2006_.

src/transform.ts

@@ -9,7 +9,7 @@ import {TimeUnit} from './timeunit';
 export interface FilterTransform {
   /**
    * The `filter` property must be one of the predicate definitions:
-   * (1) a [Vega Expression](filter.html#expression) string,
+   * (1) an [expression](types.html#expression) string,
    * where `datum` can be used to refer to the current data object;
    * (2) one of the field predicates: [equal predicate](filter.html#equal-predicate);
    * [range precidate](filter.html#range-predicate), [one-of predicate](filter.html#one-of-predicate);
@@ -24,12 +24,12 @@ export function isFilter(t: Transform): t is FilterTransform {
   return t['filter'] !== undefined;
 }
 
-
 export interface CalculateTransform {
   /**
-   * A string containing a Vega Expression. Use the variable `datum` to refer to the current data object.
+   * A [expression](types.html#expression) string. Use the variable `datum` to refer to the current data object.
    */
   calculate: string;
+
   /**
    * The field for storing the computed formula value.
    */