This plugin is designed to offer formatting over an entire selection, even if that selection has paragraph breaks in the middle! However, this plugin is new and has only had limited testing. I am grateful for your patience and your bug reports!
Select the text you want to format, and use the command Format, even over multiple lines (you can change this command name and what kind of formatting to apply in Settings). Be careful not to start but not end your selection in the middle of another type of paired formatting (e.g. bold, italics, highlighting, etc.) or vise versa. If no text is selected, the command will "toggle on" the formatting, so that what you type next will be formatted.
Two formatting styles exist by default. To add a new formatting style, scroll to the bottom of the settings pane (Multi-line Formatting Plugin Options) and click the Add formatting style button.
For each formatting style, you can enter the formatting you want to apply as Left and Right. You can change the Nickname of the command so that the name in the command palette better reflects the kind of formatting you choose.
If you want to be able to select large amounts of text but not apply your formatting style to headings in that selection you can toggle Skip Headings on.
Toggling Format word if selection is empty on means that if no text is selected but the cursor is touching or inside a word (here defined as non-whitespace), the formatting will appear around the word, rather than just around the cursor, which is what occurs if this setting is toggled off. (This toggle is new to 0.4.0.)
You can delete formatting styles that you are not using by clicking the Delete this style button at the bottom of styles settings for any style.
Like any other Obsidian commands, you can assign hotkeys to the formatting style commands generated by the Multi-line Formatting plugin in the Hotkeys options (separate from the Plugin Options), including reassigning the usual Strong/Bold (Ctrl + b) and Italics/Emphasis (Ctrl + i) hotkeys to their Multi-line Formatting commands.
Again, this is an early version of this plugin which has had limited testing. Help me improve it by reporting any unexpected behaviour.
However, this plugin is not designed to work with codeblocks. In most cases, codeblock sections will be skipped, but formatting applied to codeblocks and any sections near codeblocks may not be formatted appropriately since skipping relies on the MetadataCache, which may not be up to date. Further, the behaviour when selections include code blocks embedded in list items or blockquotes will likely not be as desired (essentially, dealing with embedded code blocks has not been implemented).
Please let me know how this plugin can be improved.
A huge thank you to lynchjames, whose Note Refactor Plugin formed the base for this plugin, to THeK3nger for the Obsidian Plugin Template, to Lishid for a helpful code review, and to roshanshariff for help debugging and refactoring!