update export.md

Author: bishabosha

docs/docs/reference/other-new-features/export.md

@@ -40,7 +40,6 @@ copier.print(copier.scan())
 An export clause has the same format as an import clause. Its general form is:
 ```scala
 export path . { sel_1, ..., sel_n }
-export given path . { sel_1, ..., sel_n }
 ```
 It consists of a qualifier expression `path`, which must be a stable identifier, followed by
 one or more selectors `sel_i` that identify what gets an alias. Selectors can be
@@ -50,7 +49,8 @@ of one of the following forms:
  - A _renaming selector_ `x => y` creates aliases for all eligible members of `path` that are named `x`, but the alias is named `y` instead of `x`.
  - An _omitting selector_ `x => _` prevents `x` from being aliased by a subsequent
    wildcard selector.
- - A _wildcard selector_ creates aliases for all eligible members of `path` except for
+ - A _given selector_ `given x` has an optional type bound `x`. It creates aliases for all eligible given instances that conform to either `x`, or `Any` if `x` is omitted, except for members that are named by a previous simple, renaming, or omitting selector.
+ - A _wildcard selector_ `_` creates aliases for all eligible members of `path` except for given instances,
    synthetic members generated by the compiler and those members that are named by a previous simple, renaming, or omitting selector.
 
 A member is _eligible_ if all of the following holds:
@@ -60,8 +60,7 @@ A member is _eligible_ if all of the following holds:
    a base class of the class containing the export clause.
  - it is accessible at the export clause,
  - it is not a constructor, nor the (synthetic) class part of an object,
- - it is a given instance (or an old-style `implicit` value)
-   if and only if the export is tagged with `given`.
+ - it is a given instance (declared with `given`) if and only if the export is from a _given selector_.
 
 It is a compile-time error if a simple or renaming selector does not identify any eligible
 members.
@@ -87,6 +86,8 @@ def f: c.T = ...
 <a id="note_class"></a>
 Export clauses can appear in classes or they can appear at the top-level. An export clause cannot appear as a statement in a block.
 
+If an export clause contains a wildcard or given selector, it is forbidden for its qualifier path to refer to a package. This is because it is not yet known how to safely track wildcard dependencies to a package for the purposes of incremental compilation.
+
 (\*) Note: Unless otherwise stated, the term "class" in this discussion also includes object and trait definitions.
 
 ## Motivation
@@ -103,11 +104,21 @@ more flexible way.
 ## Syntax changes:
 
 ```
-TemplateStat   ::=  ...
-                 |  Export
-TopStat        ::=  ...
-                 |  Export
-Export         ::=  ‘export’ [‘given’] ImportExpr {‘,’ ImportExpr}
+TemplateStat      ::=  ...
+                    |  Export
+TopStat           ::=  ...
+                    |  Export
+Import            ::=  ‘import’ ImportExpr {‘,’ ImportExpr}
+ImportExpr        ::=  StableId ‘.’ ImportSpec
+ImportSpec        ::=  id
+                    |  ‘_’
+                    |  ‘given’
+                    |  ‘{’ ImportSelectors) ‘}’
+ImportSelectors   ::=  id [‘=>’ id | ‘=>’ ‘_’] [‘,’ ImportSelectors]
+                    |  WildCardSelector {‘,’ WildCardSelector}
+WildCardSelector  ::=  ‘_'
+                    |  ‘given’ [InfixType]
+Export            ::=  ‘export’ ImportExpr {‘,’ ImportExpr}
 ```
 
 ## Elaboration of Export Clauses