This is a continuation of http://forum.plantuml.net/7095 because of character limit.
http://forum.plantuml.net/3816 Stereotyped arrows
http://forum.plantuml.net/3816 Settings multiple arrow skinparams in one line
http://forum.plantuml.net/3816 skinparam componentArrowColor
http://forum.plantuml.net/3790 DATA URI as embeded image
http://forum.plantuml.net/3770 Inline set multiple styles in various diagrams
http://forum.plantuml.net/3648 Transparent color
http://forum.plantuml.net/3636 Arrows from/to class members
http://forum.plantuml.net/3621 Component diagram consumer/provider arrows
http://forum.plantuml.net/3601 Creole on class titles with as
http://forum.plantuml.net/3562 The diagram code is embedded into the PNG metadata
http://forum.plantuml.net/3558 Latex link ([[latex://]])
http://forum.plantuml.net/3505 Activity diagram end
http://forum.plantuml.net/3482 and http://forum.plantuml.net/206 skinparam sequenceMessageAlign
http://forum.plantuml.net/3448 Tree structure inside class
http://forum.plantuml.net/3424 Class attribute stereotype
http://forum.plantuml.net/3214 -eps:text flag
http://forum.plantuml.net/3188 [norank] arrow option
http://forum.plantuml.net/3166 skinparam activityArrowFontColor
http://forum.plantuml.net/3118 skinparam padding
http://forum.plantuml.net/3104 Use \ for multiline stuff
http://forum.plantuml.net/3055 Align text with \l and \r
http://forum.plantuml.net/2899 skinparam activityShape
http://forum.plantuml.net/2868 Activity diagram multiple halting states
http://forum.plantuml.net/2793 Inline coloring of partition
http://forum.plantuml.net/2792 skinparam activityArrowFontSize
http://forum.plantuml.net/2681 Swimlane alias
http://forum.plantuml.net/7119 %autonumber%
http://forum.plantuml.net/5346 Activity diagram joinspec
http://forum.plantuml.net/3672 State Diagram <<choice>>
http://forum.plantuml.net/2913 Hide private / protected / package class memebers
http://forum.plantuml.net/2538 layout_new_line
http://forum.plantuml.net/2503 Secondary group label in sequence diagram
http://forum.plantuml.net/2427 Embed diagrams in notes and other texts
http://forum.plantuml.net/2410 Multiple include paths
http://forum.plantuml.net/2398 Note on partition
http://forum.plantuml.net/2259 Class diagram --( and -0)- arrows
http://forum.plantuml.net/2259 Class diagram circle
http://forum.plantuml.net/2239 extends and implements can reference multiple nodes
http://forum.plantuml.net/1812 State inline color
http://forum.plantuml.net/1736 Multiple lollipop edges styles
http://forum.plantuml.net/1638 package name <<Card>>
http://forum.plantuml.net/1601 -gui parameter accepts a path
http://forum.plantuml.net/1525 @append
http://forum.plantuml.net/1487 ##[style]color to specify border style and color
http://forum.plantuml.net/1466 @startuml{OPTIONS}
http://forum.plantuml.net/1343 !pragma aspect
http://forum.plantuml.net/1296 skinparam minClassWidth and skinparam sameClassWidth
http://forum.plantuml.net/1265 Salt tree tables
http://forum.plantuml.net/1232 SDL shapes (some undocumented)
http://forum.plantuml.net/1206 Dot graph
http://forum.plantuml.net/1159 Choice Pseudostate in State Diagrams
http://forum.plantuml.net/1099 State diagram hide empty description
http://forum.plantuml.net/375 Embed SVG in SVG diagram
http://forum.plantuml.net/310 Sequence diagram ?-> and ->? arrows
http://forum.plantuml.net/301 Activity Beta if (...) is/equals (...) then
http://forum.plantuml.net/265 Activity Beta kill
http://forum.plantuml.net/7334 skinparam svgDimensionStyle
http://forum.plantuml.net/7287 automatic color
http://forum.plantuml.net/7264 skinparam belowForResponse
http://forum.plantuml.net/7337 Tags
http://forum.plantuml.net/7337 remove / restore
https://github.com/plantuml/plantuml/issues/104 skinparam wrapWidth and skinparam wrapMessageWidth
https://github.com/plantuml/plantuml/pull/31 ER diagrams
https://forum.plantuml.net/3054 details on how the "attributes" vs "methods" boxes are formed, and what happens when you add your own divider line
https://forum.plantuml.net/10077 colored connectors in state diagrams
https://forum.plantuml.net/7485 diagonal-corner
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Ok, many thanks for this impressive list...
Documentation is really painfull to maintain, so we set up a collaborative way of updating it.
On each chapter of the official website (for example https://plantuml.com/en/sequence-diagram ) there are links which allow you to modify the documentation using Markdown, Dokuwiki or Asciidoc syntax (you can choose whatever you prefer).
We are going to use your list, but you can help us if you wish.
Thanks again !