New Page: Form Validation

[drpayyne]

Purpose of this pull request

This pull request (PR) creates a new page under Frontend Developer Guide to describe the files and structure of the form validation modules present in Magento.

Affected DevDocs pages

• https://devdocs.magento.com/guides/v2.3/frontend-dev-guide/validations/form-validation.html
• https://devdocs.magento.com/guides/v2.2/frontend-dev-guide/validations/form-validation.html

Links to Magento source code

• https://github.com/magento/magento2/blob/2.4-develop/lib/web/jquery/jquery.validate.js
• https://github.com/magento/magento2/blob/2.4-develop/lib/web/mage/validation.js
• https://github.com/magento/magento2/blob/2.4-develop/lib/web/mage/validation/validation.js

whatsnew
Added a new Form Validation topic to the Frontend Developer Guide.

[devops-devdocs]

An admin must run tests on this PR before it can be merged.

[jeff-matthews]

Looking good @drpayyne! Just a few minor editorial suggestions and I think this will be ready to merge.

[keharper]

@drpayyne Don't forget to add these lines to the frontmatter

contributor_name:
contributor_link:

[drpayyne]

On it, @keharper and @jeff-matthews. Thanks!

[jeff-matthews]

Thanks @drpayyne!

[drpayyne]

Thank you, @jeff-matthews!

[jeff-matthews]

running tests

[jeff-matthews]

Tests failed on linting errors:

+ rake test:md
�[35mTesting Markdown style with mdl ...�[0m
�[31mThe Markdown linter detected 4 issue(s)�[0m
�[33msrc/guides/v2.2/frontend-dev-guide/validations/form-validation.md:15: MD001 Header levels should only increment by one level at a time
src/guides/v2.2/frontend-dev-guide/validations/form-validation.md:21: MD009 Trailing spaces
src/guides/v2.3/frontend-dev-guide/validations/form-validation.md:15: MD001 Header levels should only increment by one level at a time
src/guides/v2.3/frontend-dev-guide/validations/form-validation.md:21: MD009 Trailing spaces

A detailed description of the rules is available at https://github.com/markdownlint/markdownlint/blob/master/docs/RULES.md

[drpayyne]

@jeff-matthews, on it.

[jeff-matthews]

That fixed it @drpayyne

[jeff-matthews]

running tests

[ghost]

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