Make package: URI schema implementation dependent per latest DEP.

docs/language/dartLangSpec.tex

 \documentclass{article}
 \usepackage{epsfig}
 \usepackage{color}
 \usepackage{dart}
 \usepackage{bnf}
 \usepackage{hyperref}
 \usepackage{lmodern}
 \newcommand{\code}[1]{{\sf #1}}
 \title{Dart Programming Language  Specification \\
 {\large Version 1.10}}
@@ skipping 6887 matching lines @@
 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.
  }
  
 \LMHash{}
 A URI of the form \code{dart:$s$} is interpreted as a reference to a system library (\ref{imports}) $s$. 
  
 \LMHash{}
-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.
-}
+A URI of the form \code{package:$s$} is interpreted in an implementation specific manner.
 
 \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).
+The intent is that, during development, Dart programmers can rely on a package manager to find elements of their program. 
 }
 
 \LMHash{}
 Otherwise, any relative URI is interpreted as relative to the the location of the current library. All further interpretation of URIs is implementation dependent. 
 
 \commentary{This means it is dependent on the embedder.}
 
 
 \section{Types}
 \LMLabel{types}
@@ skipping 875 matching lines @@
 
 The invariant that each normative paragraph is associated with a line
 containing the text \LMHash{} should be maintained.  Extra occurrences
 of \LMHash{} can be added if needed, e.g., in order to make
 individual \item{}s in itemized lists addressable.  Each \LM.. command
 must occur on a separate line.  \LMHash{} must occur immediately
 before the associated paragraph, and \LMLabel must occur immediately
 after the associated \section{}, \subsection{} etc.
 
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