docs: add initial thoughts

docs/technical-design/01-initial-thoughts.md

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+# Initial thoughts
+
+## The problem
+
+When using lists and checkboxes in Markdown files as To Do lists whilst working on tasks, I’d like to have a way to easily check a checkbox once an item is complete or to uncheck it if needed.
+
+## Example
+
+This is an example of a list of Markdown checkboxes:
+
+```markdown
+- [x] A complete task
+- [ ] An incomplete task
+```
+
+## Existing approaches
+
+This could be done by entering replace mode by typing `r` followed by the appropriate character to check or uncheck the checkbox. I'd prefer though to have a consistent way to check and uncheck a checkbox where I can reuse the same function and keymap.
+
+There's an also an existing Vim plugin - [jkramer/vim-checkbox](https://github.com/jkramer/vim-checkbox) - that I could use.
+
+## Solution
+
+I’d like to create my own Neovim plugin for this written in Lua as I haven’t written one yet and it would be a good learning experience and an opportunity to start contributing to the Neovim ecosystem.
+
+There are built-in Neovim APIs to get the current window, buffer, and cursor, and to get and set lines, so it should be possible to get the current line, check or uncheck a checkbox, and update the line’s contents.
+
+Doing this would also be a good start point for other and more complicated plugins in the future.
+
+## Plugin structure
+
+I’d like to follow the same structure as [https://github.com/tjdevries/stackmap.nvim](https://github.com/tjdevries/stackmap.nvim) - a plugin that TJ and bashbunni wrote recently.
+
+This includes writing tests with [Plenary](https://github.com/nvim-lua/plenary.nvim).
+
+## Checking, unchecking and toggling
+
+I was originally thinking that there would be three public methods: `check`, `uncheck`, and `toggle`.
+
+However I don't think that there's a need to expose methods for checking and unchecking.
+
+if a checkbox is already checked or unchecked then you wouldn’t need to perform the same action again, so we just need the option to toggle a checkbox and expose a single public function.
+
+For example:
+
+```lua
+-- lua/toggle-checkbox.lua
+
+local M = {}
+
+M.toggle = function()
+  -- Toggle the checkbox.
+end
+
+return M
+```
+
+I could still create and use methods for checking and unchecking but keep them private by not adding them to the returned module.
+
+## Customisation
+
+Customisation could be done by implementing `require('toggle-checkbox').setup()` if there is anything that would be worth configuring.
+
+It would be up to the user to add a keymap to their own configuration rather than hard-coding one into the plugin.
+
+## Out of scope
+
+Features such as customising and cycling through symbols would be out of scope initially in order to keep the code minimal, but could be added at a later date if there is a need for them.