If you are referring to this screen
The textarea element has a resize element in the bottom-right corner. This element’s display depends on the browser, but resizing is possible.
Indeed we could improve all the textarea elements in Edit Macro modal by making them to have a bigger default height, using the “rows” attribute (a good value would be 5-7). Would you like to create an issue with this improvement since it was your idea?
Still, even if the new height is not good enough for the users, the resize is still there and available.
Regarding the larger screens: we are using the Bootstrap 3.3.7’s modal, and this modal caps at a width of 600px for resolutions bigger than 768px. In Bootstrap 4.x, the modals get even smaller, capping at 500px. So the width of the modals and their content will be fixed and capped for now.
Regarding the full screen: since modals are on a different/upper layer than the main interface, adding an extra / additional layer on top of modal (in order to suggest the full-screen of textarea) can be confusing for the users. Going into more than 1 stacked layer assumes the users remember in what layer and at what level they are.
Technically I don’t know how hard would be to add full-screens to textareas in that modal. @mflorea might know more. But from an usability perspective it would be confusing.
Now, we worked on this topic (Inline Macro Content Editing, see https://www.xwiki.org/xwiki/bin/view/ReleaseNotes/Data/XWiki/10.10/#HInlineMacroContentEditing) in XWiki 10.10. Currently the inline editing is done only for a limited number of macros (box, info, etc.) but maybe code macro could also be a candidate. Being able to edit the content inside the page, even using the fullscreen of the editor, would be a better solution than providing fullscreen for individual textareas in modals.
Yes, I would like suggests, selects and default examples too. There is a proposal made (example https://design.xwiki.org/xwiki/bin/view/Proposal/MacroParameters#HMacro:Chart), but we are not currently working on it, and I am not sure how hard it is to implement. Ideally, we should provide examples and good defaults for the macros so that the user can just select or even just press enter when wanting a macro.
I am not sure what this means maybe you can give more details.