Review REP 144 (ros-infrastructure#96)

* mark REP 144 active

* fix spelling

* Add statement to avoid double underscore in package name

Addresses [this comment](ros-infrastructure#96 (comment))

* Clarify the structure of the mandatory rules
Separate the definition.
Bold the rules to differentiate them from the explaination.
Update some rationales

* Add justification for lowercase
Update post history date

* add lowercase callout in rule and update post date

Author: tfoote

rep-0144.rst

@@ -1,11 +1,11 @@
 REP: 144
 Title: ROS Package Naming
 Author: Vincent Rabaud <[email protected]>
-Status: Draft
+Status: Active
 Type: Informational
 Content-Type: text/x-rst
 Created: 28-Jan-2015
-Post-History:
+Post-History: 21-Dec-2018
 
 Abstract
 ========
@@ -22,7 +22,7 @@ Over time, the lack of naming conventions created problems like use of
 unexplained acronyms or packages with the same functionality but different names.
 
 For now, ROS package names translate directly to packages in supported Operating
-Systems: therefore, there is a flat global namerspace in which rules have to
+Systems: therefore, there is a flat global namespace in which rules have to
 be followed.
 
 This REP proposes rules to name a ROS package properly.
@@ -31,42 +31,57 @@ Some of those rules are mandatory, others merely advised.
 Package Naming
 ==============
 
-Mandatory Rules
----------------
-
 By habit, a package name is often used as a namespace (in C++ or any other language).
 Thus, the naming rules have to be strict.
 
+Definitions
+-----------
+
 * ``alphanumerics`` are ``a-z0-9`` only
 * ``alphabetics`` are ``a-z`` only
-* it must only consist of alphanumerics and ``_`` separators.
-  Other symbols might not be supported by some OSes (e.g. unicode characters) or would
-  make it hard to follow OSes conventions/
-* they must be at least two characters long and must start with an alphabetic character.
+
+For clarity these are both specifically exclusively lowercase.
+
+
+Mandatory Rules
+---------------
+
+**A name must:**
+
+* **only consist of lowercase alphanumerics and _ separators and start with an alphabetic character.**
+  This allows it to be used in generated symbols and functions in all supported languages.
+  Lowercase is required because the names are used in directories and filenames and some
+  platforms do not have case sensitive filesystems.
+* **not use multiple _ separators consecutively.**
+  This allows generated symbols to use the ``__`` separator to guarenteed the avoidance
+  of collisions with symbols from other packages, for example in the message generators.
+* **be at least two characters long.**
   This rule is simply to force the name of the package to be more human understandable.
+  It's recommended to be noteably longer, see below.
 
 Global Rules
 ------------
 
-* package names should be specific enough to identify what the package does.
+* **Package names should be specific enough to identify what the package does.**
   For example, a motion planner should not be called ``planner``.
   If it implements the wavefront propagation algorithm, it might be called
   ``wavefront_planner``.
   There's obviously tension between making a name specific and keeping it from becoming
   overly verbose
-* using catchall names such as ``utils`` should be avoided as they do not scope what goes
+* **Using catchall names such as** ``utils`` **should be avoided.** They do not scope what goes
   into the package or what should be outside the package
-* a package name should not contain ``ros`` as it is redundant.
+* **A package name should not contain** ``ros`` **as it is redundant.**
   Exceptions include core packages and ROS bindings of an upstream library
   (e.g. ``moveit_ros``)
-* one of ROS's goals is to develop a canonical set of tools for making robots do
+* **The package name should describe what the package does, not where it came from.**
+  One of ROS's goals is to develop a canonical set of tools for making robots do
   interesting things.
-  The package name should describe what the package does, not where it came from.
   Then again, as stated in the rules below, ``if a package is specialized
   by an entity (lab, company, ...), prepend the name of the entity``.
   But once the package is commonly used, owned and maintained, that name can be dropped
   as the package becomes the reference
-* to check whether a name is taken, consult [2]_. If you'd like your
+* **Do not use a name that's already been taken.** 
+  To check whether a name is taken, consult [2]_. If you'd like your
   repository included in that list, see the tutorial at [3]_
 
 Naming Rules