Undocumented PlantUML features in order to document
The list comes from Issue#261 thanks to @VladimirAlexiev,
And the list of Issue#261 comes mostly from QA#7095, QA#7140 thanks to @Anthony-Gaudino, and was complemented, categorized, and converted to a task list by @VladimirAlexiev.
Then the list is here in order to put, after each item: * [[98FB98#DONE]] * [[#FFD700#TODO]] * [[#AA1111#BUG]] * [[#FF6600#deprecated]] * [[#1111AA#SEE]] * or [[#C8FBC8TBC]] and to follow and share the state of new documentation to produce.
Preprocessor, Includes, Sectioning
link::preprocessing-v2[preprocessing-v2 (old)] & link::preprocessing[preprocessing (new)]
- 
QA#6577 Ability to include blocks ("subsections") of code
 - 
QA#7838
!pragma http.proxyHost - 
QA#6289
%filename%and%filenameNoExtension% - 
QA#6199
%PLANTUML_VERSION%[[#FF6600#deprecated]][[#1111AA#SEE]] New link::preprocessing#0umqmmdy1n9yk362kjka[Builtin functions]%version() - 
QA#5968
%filedate% - 
QA#5769
%filename%and%dirpath%variables [[#FF6600#deprecated]][[#1111AA#SEE]] New link::preprocessing#0umqmmdy1n9yk362kjka[Builtin functions] - 
QA#5171 [[#98FB98#DONE]] Boolean not
!and parenthesis on!ifdef[[#98FB98#DONE]] superseded by%not()[[#1111AA#SEE]] QA#12320 - 
QA#3868 Use tilde
~to escape@startuml - 
QA#5483
@startumlfilename for automatic extensions - 
QA#4467 [[#98FB98#DONE]]
@startumlwith identifier for includes [[#98FB98#DONE]] on link::sources[source file] - 
QA#1466 [[#98FB98#DONE]]
@startuml{OPTIONS}[[#98FB98#DONE]] on link::sources[source file] - 
QA#4596
\startXXXinstead of@startXXX - 
QA#5769 [[#98FB98#DONE]]
@startdef and @enddef[[#98FB98#DONE]] on link::sources[source file] - 
QA#1525
@pause @unpause @continue @append and /' ... '/multiline comments [[98FB98#DONE]] for comments [[#C8FBC8TBC]] for pause/unpause/continue - 
QA#4266
-configparameter - 
QA#2410 Multiple include paths
 - 
QA#7337 [[98FB98#DONE]]
$Tagsto include individual pieces [[#98FB98#DONE]] for link::component-diagram[component] [[#C8FBC8TBC]] for other diagram - 
QA#7337 [[98FB98#DONE]] remove / restore [[#98FB98#DONE]] for link::component-diagram[component] [[#C8FBC8TBC]] for other diagram
 - 
wildcards in
remove / hide / restore, egremove *[[98FB98#DONE]] for link::component-diagram[component] [[#C8FBC8TBC]] for other diagram 
Running and Output
link::command-line[Command-line] [[#98FB98#DONE]]
- 
QA#4752 [[#98FB98#DONE]] Output Braille diagrams (
-tbraille) [[#98FB98#DONE]] link::command-line[command-line] - 
QA#5037 [[#98FB98#DONE]]
-pipemapparameter (HTML clickable maps): link::command-line#standard_input_output[command-line#standard_input_output] - 
QA#3562 [[#98FB98#DONE]] Diagram code is embedded in PNG metadata (
-metadata -checkmeta) - 
QA#1601 [[#98FB98#DONE]]
-guiparameter accepts a path [[#98FB98#DONE]] - 
QA#3214 [[#98FB98#DONE]]
-eps:textparameter [[#98FB98#DONE]] link::command-line[command-line] 
link::ascii-art[ASCII art] [[#98FB98#DONE]] output with -ttxt or -tutxt [[#98FB98#DONE]] link::command-line[command-line]
- 
QA#4147 [[#98FB98#DONE]]
skinparam maxAsciiMessageLength[[#98FB98#DONE]] 
link::latex[LaTeX] output with -tlatex through Tikz [[#98FB98#DONE]] link::command-line[command-line]
- 
QA#1798 latex-tikz-support anything more to document?
 - 
Latex "see result online" (eg https://www.writelatex.com/read/pgkkspzgzgpb) doesn’t work because need to migrate to overleaf
 - 
QA#6495
skinparam tikzFont - 
QA#3558 Latex link [[latex://]]
 
link::svg[SVG] output with -tsvg [[#98FB98#DONE]]
Layout
- 
QA#1343
!pragma aspect - 
QA#1226
!pragma ratio - 
QA#977
skinparam nodesep - 
QA#977
skinparam ranksep - 
QA#3188 norank arrow option
 - 
QA#8365 hidden and norank
 - 
QA#4418, QA#1132, QA#3231, QA#3111, QA#3143
!pragma horizontalLineBetweenDifferentPackageAllowed - 
QA#1296
skinparam minClassWidthandskinparam sameClassWidth - 
QA#4637
skinparam minClassWidthon sequence diagram - 
QA#2538
layout_new_linefor disconnected parts - 
QA#3118
skinparam padding - 
QA#5493
skinparam ParticipantPaddingandskinparam BoxPadding 
Text and Links
link::creole[Creole], link::link[Link], link::ascii-math[ASCII Math, JLatexMath]
- 
QA#3104 Use
\for multiline stuff - 
QA#3055 Align text with
\land\r - 
QA#3601 Creole on class titles with as
 - 
Issues#104
skinparam wrapWidthandskinparam wrapMessageWidth - 
QA#3820
skinparam tabSize - 
QA#5254 [[#98FB98#DONE]]
<plain>...</plain>to remove default text style (egskinparam classFontStyle) [[#98FB98#DONE]] link::creole#xbti2cgar0ssk362kjd9[on creole page] - 
QA#5574 [[#98FB98#DONE]] tooltip over link [[#98FB98#DONE]] Page link::link[link]
 
Images, Icons, Sprites, Shapes, Embellishments
Color [[#98FB98#DONE]]
- 
QA#3770 [[#98FB98#DONE]] Inline set of multiple colors in various diagrams (
text;line;back;header) [[#98FB98#DONE]] - 
QA#1487 [[#98FB98#DONE]]
##[style]colorof node borders: works for class and state diagrams [[#98FB98#DONE]] link::class-diagram[on class] and link::state-diagram[state] - 
QA#5340 [[#98FB98#DONE]] Inline coloring of node borders [[#98FB98#DONE]] link::use-case-diagram[on use-case]
 - 
QA#7287 [[#98FB98#DONE]] Automatic color [[#98FB98#DONE]] link::color[on color page]
 - 
QA#3648 [[#98FB98#DONE]] Transparent color [[#98FB98#DONE]] link::color[on color page]
 
Arrows
- 
QA#3636 [[#98FB98#DONE]] Arrows from/to class members [[#98FB98#DONE]]
 - 
QA#3621 Component diagram consumer/provider arrows
 - 
make sure all arrow params are documented:
dotted|dashed|plain|bold|hidden|norank|single|thickness|left|right|up|down, color - 
QA#3816
skinparam ArrowColor, stereotyped arrows, new syntax for inline arrow style (Setting multiple arrowskinparams in one line); [[#FF6600#deprecated]] (componentArrowColor is deprecated) - 
QA#4949 [[#98FB98#DONE]] Inline setting for edge style and thickness [[#98FB98#DONE]] on Class and Deployment
 - 
QA#4260 [[#98FB98#DONE]] bold and plain arrow styles [[#98FB98#DONE]]
 - 
QA#4181 [[#98FB98#DONE]] bold, dashed, dotted [[#98FB98#DONE]]
 - 
Make sure all arrow types are documented on one page: See
arrowsandarrows-2at github.com/anoff/blog/tree/master/static/assets/plantuml/diagrams - 
QA#1736 [[#98FB98#DONE]] Multiple lollipop edge styles [[#98FB98#DONE]]
 - 
QA#5261 Crows foot edge
 - 
QA#2259 [[#98FB98#DONE]] Class diagram
--(and-0)-arrows [[#98FB98#DONE]] - 
QA#310 [[#98FB98#DONE]] Sequence diagram
?->and->?arrows [[#98FB98#DONE]] 
Alternative Layoters
- 
QA#4436, QA#5336, link::smetana02[smetana02] [[#98FB98#DONE]]
!pragma graphviz_dot jdot: replace graphviz with Java code [[#98FB98#DONE]] ➥!pragma layout smetanaSee link::smetana02[smetana02] - 
link::vizjs[vizjs]
-graphvizdot vizjs: replace graphviz with JavaScript code - 
noditaa: replace ditaa with java code
 
link::class-diagram[Class Diagrams]
- 
QA#5835 [[#98FB98#DONE]] Notes on class fields [[#98FB98#DONE]]
 - 
QA#3054 details on how the "attributes" vs "methods" boxes are formed, and what happens when you add your own divider line
 - 
QA#2913 Hide private / protected / package class members
 - 
QA#3448 [[#98FB98#DONE]] Tree structure inside class [[#98FB98#DONE]] See link::creole#2u7lnfjrnmfdk362kjda[creole tree]
 - 
QA#3424 Class attribute stereotype
 - 
QA#2259 Class diagram circle
 - 
QA#2239 extends and implements can reference multiple nodes
 - 
QA#3193
skinparam groupInheritanceto merge inheritance arrows going to the same parent [[#98FB98#DONE]] (+ Adding link to Defect QA#13532) - 
QA#1638 [[98FB98#DONE]] package style card [[#98FB98#DONE]] [[#C8FBC8TBC]]
 
link::sequence-diagram[Sequence Diagrams] [[#98FB98#DONE]]
link::teoz[teoz], link::sequence-diagram#anchors_and_duration[sequence-diagram#anchors_and_duration], tag/teoz: new Teoz (vs old Puma) for sequence diagrams
- 
QA#4247 [[#98FB98#DONE]] hide unlinked participants [[#98FB98#DONE]]
 - 
QA#7119 [[#98FB98#DONE]]
%autonumber% - 
QA#8511 [[#98FB98#DONE]]
autonumber inc[[#98FB98#DONE]] - 
QA#2794 [[#98FB98#DONE]]
skinparam lifelineStrategy[[#98FB98#DONE]] - 
QA#2503 [[#98FB98#DONE]] Secondary group label in sequence diagram [[#98FB98#DONE]]
 - 
QA#7264 [[#98FB98#DONE]]
skinparam belowForResponse[[#98FB98#DONE]] - 
QA#1047 [[#98FB98#DONE]]
skinparam style strictuml: emits triangle rather than sharp arrow heads [[#98FB98#DONE]] - 
QA#3482, QA#206 [[#98FB98#DONE]]
skinparam sequenceMessageAlign[[#98FB98#DONE]] 
link::activity-diagram-beta[Activity Diagrams]
- 
QA#5201
skinparam swimlaneWidth[[#AA1111#BUG]] See QA#12463 - 
QA#2681 [[#98FB98#DONE]] Swimlane alias [[#98FB98#DONE]]
 - 
QA#4470 [[#98FB98#DONE]] Label of arrows of repeat loops (repeat while) [[#98FB98#DONE]]
 - 
QA#6105 [[#98FB98#DONE]] Activity diagram
break[[#98FB98#DONE]] - 
QA#301 [[#98FB98#DONE]] Activity Beta
if (...) is/equals (...) then[[#98FB98#DONE]] - 
QA#265 [[#98FB98#DONE]] Activity Beta
kill[[#98FB98#DONE]] - 
QA#3931 [[#98FB98#DONE]]
!pragma useVerticalIf on: draw if/elseif/else structure vertically [[#98FB98#DONE]] - 
QA#1626 [[#98FB98#DONE]] Activity diagram GOTO [[#98FB98#DONE]] See link::activity-diagram-beta[activity-diagram] and link::activity-diagram-issues[activity-diagram-issues]
 - 
QA#2792
skinparam activityArrowFontSize - 
QA#3166
skinparam activityArrowFontColor - 
QA#5346 [[#98FB98#DONE]] Activity diagram joinspec [[#98FB98#DONE]]
 - 
QA#2868 Activity diagram multiple halting states
 - 
QA#3505 [[#98FB98#DONE]] Activity diagram end [[#98FB98#DONE]]
 - 
QA#5826 Backward on loops
 - 
QA#4906 [[#98FB98#DONE]] Gradient color on activity diagram partition [[#98FB98#DONE]]
 - 
QA#2398 [[#98FB98#DONE]] Note on partition [[#98FB98#DONE]]
 - 
QA#2793 [[#98FB98#DONE]] Inline coloring of partition [[#98FB98#DONE]]
 - 
QA#1290 [[#98FB98#DONE]]
skinparam conditionStyle: inside (hexagon: default), foo1 (big diamond), diamond (tiny diamond) [[#98FB98#DONE]] - 
QA#6010
skinparam arrowMessageAlign center - 
QA#4411
skinparam colorArrowSeparationSpace: multiple parallel arrows in activity digrams - 
[[#98FB98#DONE]] QA#3770 Background color of
alt/group→ to link::sequence-diagram[Sequence Diagrams] 
link::state-diagram[State Diagrams] [[#98FB98#DONE]]
- 
QA#1159 [[#98FB98#DONE]] State diagram
<<choice>>, <<fork>>, <<join>>, <<end>>[[#98FB98#DONE]] - 
QA#3672 [[#98FB98#DONE]] State Diagram
<<choice>>[[#98FB98#DONE]] - 
QA#10077 [[#98FB98#DONE]] Colored connectors in state diagrams [[#98FB98#DONE]]
 - 
QA#1159 [[#98FB98#DONE]] Choice Pseudostate in State Diagrams [[#98FB98#DONE]]
 - 
QA#1099 [[#98FB98#DONE]] State diagram hide empty description [[#98FB98#DONE]]
 - 
QA#4309 [[#98FB98#DONE]] State diagram
+[expansionInput] and [expansionOutput], [inputPin] and [outputPin], [entrypoint] and [exitpoint] +[[#98FB98#DONE]] - 
QA#1812 [[#98FB98#DONE]] State inline color [[#98FB98#DONE]]
 
link::timing-diagram[Timing Diagrams] [[#98FB98#DONE]]
- 
QA#5776 [[#98FB98#DONE]] Timing diagram coloring [[#98FB98#DONE]]
 
link::bpmn[BPMN Diagrams] [[#98FB98#DONE]]
- 
QA#5647 [[#98FB98#DONE]] BPMN (
@startbpmand@endbpm) [[#98FB98#DONE]] Page link::bpmn[BPMN] updated 
link::wbs-diagram[WBS Diagrams]
Work Breakdown Structures, Organizational Breakdown Structures (organigrams)