I have an action with a rather large text content. When editing the text, it is actually possible to resize the text input field. But once you click return, the action is shown in it’s original default size. And the text flows out of the action’s bounding box.
It should be possible to resize actions.
I assume you mean Activity when mentioning Action.
It is debatable whether or not resizing activities is something good or not because size always transport additional semantics (i.e. bigger = more important). That is why we do not allow resizing activities per default. We may change our minds in the future though.
You can do two things to circumvent this issue at the current point in time:
Roll your own BPMN Modeler using our toolkit and allow resizing of tasks. This extension, for example, makes your tasks resizable.
Use shorter labels
If I were empowered to vote, then I’d vote for supporting activity sizing 
One of the primary purposes for the BPMN diagram is to convey the process to a wide audience - and sometimes more than a short label is necessary to do that. This is especially important in static presentations.
With an interactive presentation - the option of displaying more text during a mouse over is an attractive option that addresses the same concern.
In BPMN we have the text annotation that should cover all kinds of use cases in the area of providing additional documentation.
BPMN does not specify anything in regards to activity sizing. Limiting sizing is not a BPMN issue but one of the software designer’s view of how you should use the software. It’s obvious Camunda believes it knows best how you should use the software to fit your needs.
If making acitivites resizable is asking too much, at least consider dynamically resizing the box as the text increases to avoid ugly overflow. Alternatively, add a text wrapping option (overflow / wrap / clip) like in a spreadsheet.
Consider using text annotations to convey additional details.
Ah that’s very useful. I’d still like to resize activities. 
It would be great, if you would allow it to resize the activities itself (manually like the annotations) - your solution with the annotations is not suitable for our case. Otherwise i will be forced to use another tool which i really does not want to.
I understand your point of view about it, but it feels that your point of view is forcing me to do it the way you are seeing it which makes me feel uncomfortable.