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 5013 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 whose URI begins with \code{dart:}. Any other library is {\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 an import of a  system library and an import of a non-system library:

[kasperl, 2014/03/24 07:48:14]

I don't think this is enough. We need to talk about the element that the name N
refers to. If the name would be introduced into the top-level scope of L by the
import of a library I1 and another library I2 and that the definition of N
pulled in via the import of I1 is (indirectly through potentially long re-export
chains) from a system library then we want to hide the name N on the import of
I1.

 \begin{itemize}
-\item The import from \code{dart:} is implicitly extended by a \code{\HIDE{} $N$} clause.
+\item The import of the system library 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 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 the system library 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 734 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}