Pattern catalog

Patterns are common ways of doing things, like recipes. People have patterns for solving equations, making web pages, wrapping gifts, all sorts of things. Part of learning a skill is learning the patterns that help you be more effective.

Here are patterns on this website. This list can help you find the patterns you need to do a task.

Name	Tags	Summary	Where referenced
Single-field validation		Set an error message variable to MT. For each check (is the data numeric, too small, etc.): Check that the error message variable is still MT. If it is... Test the input data. If it fails, set the error message variable. Repeat for each check. Later, if error message variable is not MT, show it, and skip processing.
Validation chain	Validation	Test some input, making an error message if needed. If that's OK, run another test. If it's still OK, do another.	Validation basics