1 files changed, 9 insertions, 2 deletions
diff --git a/doc/manual.tex b/doc/manual.tex
index 76f69330..b65809d0 100644
--- a/doc/manual.tex
+++ b/doc/manual.tex
@@ -151,7 +151,7 @@ Here is the complete list of directive forms.  ``FFI'' stands for ``foreign func
 \item \texttt{exe FILENAME} sets the filename to which to write the output executable.  The default for file \texttt{P.urp} is \texttt{P.exe}.
 \item \texttt{file URI FILENAME} asks for the application executable to respond to requests for \texttt{URI} by serving a snapshot of the contents of \texttt{FILENAME} as of compile time.  That is, the file contents are baked into the executable.  System file \texttt{/etc/mime.types} is consulted (again, at compile time) to figure out the right MIME type to suggest in the HTTP response.
 \item \texttt{ffi FILENAME} reads the file \texttt{FILENAME.urs} to determine the interface to a new FFI module.  The name of the module is calculated from \texttt{FILENAME} in the same way as for normal source files.  See the files \texttt{include/urweb/urweb\_cpp.h} and \texttt{src/c/urweb.c} for examples of C headers and implementations for FFI modules.  In general, every type or value \texttt{Module.ident} becomes \texttt{uw\_Module\_ident} in C.
-\item \texttt{html5} activates work-in-progress support for generating HTML5 instead of XHTML.  For now, this option only affects the first few tokens on any page, which are always the same.
+\item \texttt{html5} asks to generate HTML5 code, which primarily affects the first few lines of the output documents, like the \texttt{DOCTYPE}.  This option is on by default.
 \item \texttt{include FILENAME} adds \texttt{FILENAME} to the list of files to be \texttt{\#include}d in C sources.  This is most useful for interfacing with new FFI modules.
 \item \texttt{jsFile FILENAME} asks to serve the contents of a file as JavaScript.  All such content is concatenated into a single file, included via a \texttt{<script>} tag on every page that needs client-side scripting.
 \item \texttt{jsFunc Module.ident=name} gives the JavaScript name of an FFI value.
@@ -192,6 +192,7 @@ Here is the complete list of directive forms.  ``FFI'' stands for ``foreign func
 \item \texttt{sql FILENAME} sets where to write an SQL file with the commands to create the expected database schema.  The default is not to create such a file.
 \item \texttt{timeFormat FMT} accepts a time format string, as processed by the POSIX C function \texttt{strftime()}.  This controls the default rendering of $\mt{time}$ values, via the $\mt{show}$ instance for $\mt{time}$.
 \item \texttt{timeout N} sets to \texttt{N} seconds the amount of time that the generated server will wait after the last contact from a client before determining that that client has exited the application.  Clients that remain active will take the timeout setting into account in determining how often to ping the server, so it only makes sense to set a high timeout to cope with browser and network delays and failures.  Higher timeouts can lead to more unnecessary client information taking up memory on the server.  The timeout goes unused by any page that doesn't involve the \texttt{recv} function, since the server only needs to store per-client information for clients that receive asynchronous messages.
+\item \texttt{xhtml} asks to generate XHTML code, which primarily affects the first few lines of the output documents, like the \texttt{DOCTYPE}.
 \end{itemize}
 
 
@@ -2095,6 +2096,12 @@ Configure the policy for meta names with the \texttt{allow} and \texttt{deny} \t
 
 Ur/Web supports running code on web browsers, via automatic compilation to JavaScript.
 
+The concurrency model is \emph{cooperative multithreading}.  Like with, say, POSIX threads, which uses the \emph{preemptive multithreading} model, there may be multiple threads of control active at a time.  However, unlike with preemptive multithreading, the currently running thread gets to run interrupted until a well-defined \emph{context-switch} point.  Specifically, four functions defined below are the context-switch points.  They are $\mt{sleep}$, $\mt{rpc}$, $\mt{tryRpc}$, and $\mt{recv}$.  (We explain their purposes as we come to them below.)  Additional functions added via the foreign function interface might also have context-switching behavior.  In any case, it is guaranteed that a running thread ``owns the processor'' until it calls a context-switching function, at which time we may switch to running a different thread instead.
+
+This concurrency paradigm has many nice properties.  For instance, there is almost never any need for locking or other synchronization between threads.
+
+Readers used to the standard JavaScript model may recognize this style as the natural one that we obtain by imposing a thread-based perspective on top of the usual JavaScript callback-based API.  Indeed, every context-switching Ur/Web function is implemented with an underlying JavaScript call that asks for some callback to be triggered when an event happens.
+
 \subsubsection{The Basics}
 
 All of the functions in this subsection are client-side only.
@@ -2245,7 +2252,7 @@ The $\mt{channel}$ and $\mt{send}$ operations may only be executed on the server
 
 Clients and channels live only as long as the web browser page views that they are associated with.  When a user surfs away, his client and its channels will be garbage-collected, after that user is not heard from for the timeout period.  Garbage collection deletes any database row that contains a client or channel directly.  Any reference to one of these types inside an $\mt{option}$ is set to $\mt{None}$ instead.  Both kinds of handling have the flavor of weak pointers, and that is a useful way to think about clients and channels in the database.
 
-\emph{Note}: Currently, there are known concurrency issues with multi-threaded applications that employ message-passing on top of database engines that don't support true serializable transactions.  Postgres 9.1 is the only supported engine that does this properly.
+\emph{Note}: Currently, there are known concurrency issues with multi-threaded applications that employ message-passing on top of database engines that don't support true serializable transactions.  Postgres (versions 9.1 and up) is the only supported engine that does this properly.
 
 
 \section{Ur/Web Syntax Extensions}