Clarify that dart system libs have lower priority regardless how imported.

docs/language/dartLangSpec.tex

 \documentclass{article}
 \usepackage{epsfig}
 \usepackage{dart}
 \usepackage{bnf}
 \usepackage{hyperref}
 \newcommand{\code}[1]{{\sf #1}}
 \title{Dart Programming Language  Specification \\
 {\large Version 1.3}}
 %\author{The Dart Team}
 \begin{document}
@@ skipping 1890 matching lines @@
    sort(List$<$T$>$ l) {... l[n] $<$ l[n+1] ...}
 \}
 
 \end{dartCode}
 
 \commentary{
 Even where type parameters are in scope there are numerous restrictions at this time:
 \begin{itemize}
 \item A type parameter cannot be used to name a constructor in an instance creation expression (\ref{instanceCreation}).
 \item A type parameter cannot be used as a superclass or superinterface (\ref{superclasses}, \ref{superinterfaces}, \ref{interfaceSuperinterfaces}).
-\item A type parameter cannot be used as a generic.
+\item A type parameter cannot be used as a generic type.
 \end{itemize}
 
 The normative versions of these  are given in the appropriate sections of this specification. Some of these restrictions may be lifted in the future.
 }
 
+
 %A generic has a type parameter scope. The enclosing scope of a type parameter scope of a generic G  is the enclosing scope of G.
 
 
 %class T {...}
 
 %class G<T> extends T;
 
 %By current rules, this is illegal. Make sure we preserve this.
 
 
@@ skipping 3097 matching lines @@
 
 Then, for each entry mapping key $k$ to declaration $d$ in $NS$,  $d$ is made available in the top level scope of $L$ under the name $k$ unless either:
 \begin{itemize}
 \item
 a top-level declaration with the name $k$ exists in $L$, OR
 \item a prefix clause of the form  \AS{} $k$ is used in $L$.
 \end{itemize}
 
 \rationale{The greatly increases the chance that a member can be added to a library without breaking its importers.}
 
-If a name $N$ is referenced by a library $L$ and $N$ would be introduced into the top level scope of $L$ by an import from a library whose URI begins with \code{dart:} and an import from a library whose URI does not begin with \code{dart:}:
+A {\em system library} is a library that is part of the Dart implementation. Any other library is a {\em non-system library}. If a name $N$ is referenced by a library $L$ and $N$ would be introduced into the top level scope of $L$ by 
+imports of two libraries, $L_1$ and $L_2$, and the exported namespace of $L_1$ binds $N$ to a declaration originating in a system library:
+
+%an import of a  system library and an import of a non-system library:
 \begin{itemize}
-\item The import from \code{dart:} is implicitly extended by a \code{\HIDE{} $N$} clause.
+\item The import of $L_1$ is implicitly extended by a \code{\HIDE{} $N$} clause.
 \item A static warning is issued.
 \end{itemize}
 
 \rationale {
 Whereas normal conflicts are resolved at deployment time, the functionality of \code{dart:} libraries is injected into an application at run time, and may vary over time as browsers are upgraded.  Thus, conflicts with \code{dart:} libraries can arise at runtime, outside the developerÕs control. To avoid breaking deployed applications in this way, conflicts with the \code{dart:} libraries are treated specially.
 
 It is recommended that tools that deploy Dart code produce output in which all imports use show clauses to ensure that additions to the namespace of a library never impact deployed code.
 }
 
 If a name $N$ is referenced by a library $L$ and $N$ is  introduced into  the top level scope of $L$ by more than one import, and not all the imports denote the same declaration, then:
@@ skipping 79 matching lines @@
 
 $NS_i = \SHOW{}([id_1, \ldots, id_k], NS_{i-1}$).  
 \item If $C_i$ is of the form \code{\HIDE{} $id_1, \ldots, id_k$} 
 
 then let $NS_i = \HIDE{}([id_1, \ldots, id_k], NS_{i-1}$). 
 \end{itemize}
 
 For each
 entry mapping key $k$ to declaration $d$ in $NS_n$ an entry mapping $k$ to $d$ is added to the exported namespace of $L$ unless a  top-level declaration with the name $k$ exists in $L$.  
 
-If a name $N$ is referenced by a library $L$ and $N$ would be introduced into the exported namespace of $L$ by an export from a library whose URI begins with \code{dart:} and an export from a library whose URI does not begin with \code{dart:}:
+If a name $N$ is referenced by a library $L$ and $N$ would be introduced into the exported namespace of $L$ by exports of two libraries, $L_1$ and $L_2$, and the exported namespace of $L_1$ binds $N$ to a declaration originating in a system library:
+%an export of a system library and an export of a non-system library:
 \begin{itemize}
-\item The export from \code{dart:} is implicitly extended by a \code{\HIDE{} $N$} clause.
+\item The export of $L_1$ is implicitly extended by a \code{\HIDE{} $N$} clause.
 \item A static warning is issued.
 \end{itemize}
 
 \rationale{
 See the discussion in section \ref{imports} for the reasoning behind this rule.
 }
 
 We say that $L$ {\em re-exports library } $B$, and also that $L$ {\em re-exports namespace } $NS_n$. When no confusion can arise, we may simply state that $L$ {\em re-exports }$B$, or that $L$ {\em re-exports }$NS_n$.
 
 It is a compile-time error if a name $N$ is re-exported by a library $L$ and $N$ is  introduced into the export namespace of $L$ by more than one export, unless all  exports refer to same declaration for the name $N$.  It is a static warning to export two different libraries with the same name.
@@ skipping 52 matching lines @@
 \end{grammar}
 
 It is a compile-time error if  the string literal $x$ that describes a URI is not a compile-time constant, or if $x$ involves string interpolation.
  
 This specification does not discuss the interpretation of URIs, with the following exceptions. 
  
  \rationale{
  The interpretation of URIs is mostly left to the surrounding computing environment. For example, if Dart is running in a web browser, that browser will likely interpret some URIs. While it might seem attractive to specify, say, that URIs are interpreted with respect to a standard such as IETF RFC 3986, in practice this will usually depend on the browser and cannot be relied upon.
  }
  
-A URI of the form \code{dart:$s$} is interpreted as a reference to a library $s$ that is part of the Dart implementation. 
+A URI of the form \code{dart:$s$} is interpreted as a reference to a system library (\ref{imports}) $s$. 
  
 A URI of the form \code{package:$s$} is interpreted as a URI of the form \code{packages/s} relative to an implementation specified location.
 
 \commentary{ 
 This location will often be the location of the root library presented to the Dart compiler. However, implementations may supply means to override or replace this choice.
 }
 
 \rationale{
 The intent is that, during development, Dart programmers can rely on a package manager to find elements of their program. Such package managers may provide a directory structure starting at a local directory \code{packages} where they place the required dart code (or links thereto).
 }
@@ skipping 661 matching lines @@
 \item The names of compile time constant variables never use lower case letters. If they consist of multiple words, those words are separated by underscores. Examples: PI,  I\_AM\_A\_CONSTANT.
 \item The names of functions (including getters, setters, methods and local or library functions) and non-constant variables begin with a lowercase letter. If the name consists of multiple words, each  word (except the first) begins with an uppercase letter.  No other uppercase letters are used. Examples: camlCase, dart4TheWorld
 \item The names of types (including classes and type aliases) begin with an upper case letter.  If the name consists of multiple words, each  word  begins with an uppercase letter.  No other uppercase letters are used. Examples: CamlCase, Dart4TheWorld.
 \item The names of type variables are short (preferably single letter). Examples: T, S, K, V , E.
 \item The names of libraries or library prefixes never use upper case letters. If they consist of multiple words, those words are separated by underscores. Example: my\_favorite\_library.
 \end{itemize}
 }
 
 
 \end{document}