Drupal's core options module provides fields to create a select list (existing of integers, floats or strings).

Like contributed modules, dependencies of a custom module can also be installed by providing a composer.json file in the directory of the custom module. This provides a neat solution to ensure that external libraries/modules are available in the correct place, without overloading the root (projects) composer.json file.

When writing custom forms, you are often asked to add an extra paragraph of text between input fields. A solution that is used a lot is:

When you're, like me, using Windows as your development environment, letting your Drupal environment send mails can be a big challenge. This in contrast to a Linux/Mac OS X based system, where it is much easier to send mails. I think too easy...

Often when already existing pages/forms have to be changed, you simply use one of the alter hooks to add the needed extra functionality. However, sometimes you want, or are forged, to overwrite an already existing page completely.