regular-expressions

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sed -n '<from>,<to>p' SKILL.md one section rather than reading the file; ./mxcli syntax <topic> answers how do I write this for a fraction of either.

lines	section
26-32	When to Use This Skill
33-58	What a Mendix regular expression is
59-68	Writing the pattern
69-83	Go cannot check every legal pattern
84-142	Binding a regex to an attribute
143-155	Finding out who uses one
156-167	Common Mistakes
168-173	Related
174-176	Regular expressions (LIST/DESCRIBE/CREATE [OR MODIFY]/DROP REGULAR EXPRESSION)

Regular Expressions

When to Use This Skill

Use this skill when the user wants to:

• Add a named validation pattern (email, phone, identifier, postcode)
• See or change the regexes a project already has
• Understand why a regex cannot be attached to an attribute from MDL

What a Mendix regular expression is

A document, not a string on a rule. An attribute validation rule stores a reference to it by qualified name, so one pattern is shared by every attribute that validates against it. That is why it gets a create statement of its own.

mdl 1;
list regular expressions;
list regular expressions in Val;
describe regular expression Val.EmailAddress;   -- re-executable MDL

/** A, not too restrictive, email address regular expression */
create regular expression Val.EmailAddress (
  Expression: '\w+((-|\+|\.)\w+)*@\w+([\.-]?\w+)*(\.\w{2,})+'
);

drop regular expression Val.EmailAddress;

Property	Meaning	Default
Expression	the pattern — required	—
Documentation	free text	none
ExportLevel	Hidden or API (Public is a deprecated spelling of API, MDL-DEPR161)	Hidden

Writing the pattern

The pattern is an ordinary MDL string:

• Backslashes are NOT escape characters. Write \d, \w, \. exactly as Mendix should see them — do not double them.
• A single quote is doubled, like any MDL string: '^it''s$'.
• Commas, braces and pipes inside the pattern are fine — the whole thing is one quoted string.