Libraries can be private.

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 1.11}}
+{\large Version 1.2}}
 \author{The Dart Team}
 \begin{document}
 \maketitle
 
 \tableofcontents
 
 
 \newpage
 
 \pagestyle{myheadings}
@@ skipping 190 matching lines @@
 \subsection{Privacy}
 \label{privacy}
 
 Dart supports two levels of privacy: {\em public} and {\em private}. A declaration is {\em private} iff its name begins with an underscore (the \_ character) otherwise it is {\em public.} 
 A declaration $m$ is {\em accessible to library $L$}  if $m$ is declared in $L$ or if $m$ is public.
 
 \commentary{
 This means private declarations may only be accessed within the library in which they are declared.
 }
 
-Privacy applies only to declarations within a library, not to library declarations themselves. 
-
-\rationale{
-Libraries do not reference each other by name and so the idea of a private library is meaningless.
-Thus, if the name of a library begins with an underscore, it has no special significance.
-}
 

[Lasse Reichstein Nielsen, 2014/02/14 11:48:26]

With this change, a library name declaration is private if it *begins* with an
underscore. 
That is,
  library _foo;
and 
  library _foo.bar;
are private names of libraries.

What is the meaning of:
  library foo._bar;
The "_bar" is an indentifier (per the grammar), but is not the name of a
declaration, and the name in total doesn't start with an underscore.
That would mean that "foo._bar" is not a private name, and the "_bar" part
should not be be name-mangled for privacy (the VM currently does that).

(This is perfectly fine, and easy to implement, I just want to be sure I
understand the consequences).

 \rationale{Privacy is, at this point, a static notion tied to a particular piece of code (a library). It is designed to support software engineering concerns rather than security concerns. Untrusted code should always run in an another isolate.  It is possible that libraries will become first class objects and privacy will be a dynamic notion tied to a library instance.
 
 Privacy is indicated by the name of a declaration - hence privacy and naming are not orthogonal. This has the advantage that both humans and machines can recognize access to private declarations at the point of use without knowledge of the context from which the declaration is derived.}
 
 \subsection{Concurrency}
 
 Dart code is always single threaded. There is no shared-state concurrency in Dart. Concurrency is supported via actor-like entities called {\em isolates}.
 
 An isolate is a unit of concurrency. It has its own memory and its own thread of control. Isolates communicate by message passing (\ref{sendingMessages}). No state is ever shared between isolates. Isolates are created by spawning (\ref{spawningAnIsolate}).
 
@@ skipping 4589 matching lines @@
 
 %\end{dartCode}
 
 %\rationale{therefore, we opt for the second option. Alternately, one could insist that assert be a reserved word, which may have an undesirable effect with respect to compatibility of Javascript code ported to Dart.}
 
 \section{Libraries and Scripts}
 \label{librariesAndScripts}
 
 A Dart program consists of one or more libraries, and may be built out of one or more {\em compilation units}. A compilation unit may be a library or a part (\ref{parts}). 
 
-A library consists of (a possibly empty) set of imports, a set of exports, and a set of top-level declarations. A top-level declaration is either a class (\ref{classes}), a type alias declaration (\ref{typedef}), a function (\ref{functions}) or a variable declaration (\ref{variables}). The members of a library $L$ are those top level declarations given within a $L$.
+A library consists of (a possibly empty) set of imports, a set of exports,  and a set of top-level declarations. A top-level declaration is either a class (\ref{classes}), a type alias declaration (\ref{typedef}), a function (\ref{functions}) or a variable declaration (\ref{variables}). The members of a library $L$ are those top level declarations given within a $L$.
 
  \begin{grammar}
 {\bf topLevelDefinition:}classDefinition;
 %      classDefinitionOrInterfaceInjection;
 %      interfaceDefinitionOrInterfaceInjection;
  %     mixinApplication;
       typeAlias;
       \EXTERNAL{}? functionSignature `{\escapegrammar ;}';
       \EXTERNAL{}? getterSignature `{\escapegrammar ;}';
       \EXTERNAL{}? setterSignature `{\escapegrammar ;}';      
@@ skipping 984 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}