anchor.diff:  // Level 1 -->
   == System Purpose
   
  -The purpose of the Focus/Vaporpad system is to be a trustworthy text-field/text-editor synchronization service.
  +The purpose of the Focus system is to provide a trustworthy real-time collaborative editing service for a rich document model suitable for representing text, drawings, spreadsheets, and forms.
   
   [[T-1]]
   .T-1: Target Operating Environment
  -Vaporpad is intended to be run either on the internet or on a private network of 2014: that is, over IPv4 or v6, TCP, TLS, HTTP/1.1 or HTTP/2 and with access to renderers for HTML5, JS, CSS3, WebSockets, etc.
  +Focus is intended to be run either on the internet or on a private network of 2014: that is, over IPv4 or v6, TCP, TLS, HTTP/1.1 or HTTP/2 and with access to renderers for HTML5, JS, CSS3, WebSockets, etc.
   
   [[T-2]]
   .T-2: Target Hardware
  -Vaporpad is intended to run on Debian Jessie and Mac OS 10.9 on machines with at least 1G available RAM, 1G available diskspace, and 1 available >1GHz CPU core.
  +Focus is intended to run on Debian Jessie and Mac OS 10.9 on machines with at least 1G available RAM, 1G available diskspace, and 1 available >1GHz CPU core.
   
   [[T-3]]
   .T-3: Target Interfaces
  -Vaporpad will speak HTTP/1.1 on machines with 1 network interface, 1 IPv4 or IPv6 address, and 1 TCP port.
  +Focus will speak HTTP/1.1 on machines with 1 network interface, 1 IPv4 or IPv6 address, and 1 TCP port.
   
   [[T-4]]
   .T-4: Target Audience
  -Vaporpad is intended to work for distributors, operators, integrators, editors, viewers, contributors, and researchers.
  +Focus is intended to work for distributors, operators, integrators, editors, viewers, contributors, and researchers.
   
   === High-Level System Diagram
   
  
positive.code: 
  [[N-D-1]]
  .N-D-1: Freedom
  As a distributor, I want Vaporpad to be https://www.debian.org/social_contract=guidelines[DFSG-free software].
  
  [[N-D-2]]
  .N-D-2: Maintainability
  As a distributor, I want Vaporpad to be easy to package. ↑<<A-5>>
  
  [[N-D-3]]
  .N-D-3: Upstream Support
  As a distributor, I want Vaporpad to be maintained. ↑<<A-5>>
  
  [[N-D-4]]
  .N-D-4: Upstream Availability
  As a distributor, I want to know how to reach the Vaporpad maintainers.
  
  [[N-D-5]]
  .N-D-5: Release Notification
  As a distributor, I want to know how to subscribe to news about new Vaporpad releases.
  
  === Operators
  
  
negative.code: 
  [[PR-1]]
  .PR-1: Client-Server Architecture
  Focus will use a client-server architecture. ↑[<<N-O-11>>, <<N-I-2>>]
  
  [[PR-2]]
  .PR-2: Reference Code + Protocol
  Focus includes reference client code, reference server code, and a ↓<<protocol#protocol-overview,documented protocol>> spoken between them. ↑[<<N-I-2>>]
  
  [[PR-3]]
  .PR-3: Operational Transformation Theory
  Focus shall be based on the ↓<<ot-theory#introduction,theory of operational transformation>>.
  
  [[PR-4]]
  .PR-4: Memory-Safe Language
  Focus shall be written in a memory-safe language. ↑[<<N-O-11>>, <<N-I-2>>]
  
  [[PR-5]]
  .PR-5: Certified Algorithms
  Where easy, core Focus algorithms (or their cousins) shall be certified correct w.r.t. this specification. ↑<<N-I-2>>
  
  [[PR-6]]
  .PR-6: Protocol Purpose
  