# How to - [Validate inputs](https://documentation.alpaco.email/how-to/validate-inputs.md): Validating inputs and warning the user is an essential part of handing over your template to others users - [Subject line & Preheader](https://documentation.alpaco.email/how-to/subject-line-and-preheader.md): Subject line & preheaders are a natural part of email marketing, it's the first thingbut the way it's handled and supported by the various ESP's are different - [Escape code from the editor](https://documentation.alpaco.email/how-to/escape-code-from-the-editor.md): Sometimes you want to display something for the editor, but have some other code executed on export, or sometimes you just want the code editor to leave your delicate ESP specific variables alone - [Use custom fonts](https://documentation.alpaco.email/how-to/use-custom-fonts.md): Here we'll describe how you can add custom fonts to your email campaigns and start making use of them - [AMP](https://documentation.alpaco.email/how-to/amp.md): AMP for email stands for Accelerated Mobile Pages for email and is the ability to add immersive interactions to your email. It's usually paired up with a fallback versions for non-amp inboxes --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://documentation.alpaco.email/how-to.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.