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title: Program building blocks
summary: Program building blocks in AL covers operators, statements, system-defined variables, access modifiers and XML comments. It answers questions about AL syntax, operator precedence, flow control, symbol visibility and inline code documentation.
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---

# Program building blocks

> Program building blocks in AL covers operators, statements, system-defined variables, access modifiers and XML comments. It answers questions about AL syntax, operator precedence, flow control, symbol visibility and inline code documentation.

Path: [Development](../../development.md) > [Programming in the AL language](../programming-in-the-al-language.md) > Program building blocks · tier official · system development · narrative reviewed (checked by Opus)

## Overview

This section collects the core elements used to write AL code. The reference pages cover operators, system-defined variables such as Rec and CurrPage, access modifiers for controlling visibility, and XML comments for documentation. A Statements subtopic covers simple and control statements.

Start with Statements and AL operators to learn syntax and evaluation order. Then read System-defined variables to see how code reaches the current record, page or report. Use Access Modifiers when designing APIs, and XML comments when documenting code for IntelliSense and ALDoc.

## Key points

- AL operators page lists arithmetic, comparison, logical, conditional and compound assignment operators, plus precedence (operator hierarchy).
- Statements subtopic (2 pages) covers simple statements: assignment, method calls, AssertError.
- Control statements include if-then-else, case, for, foreach, while, repeat-until, break and continue.
- System-defined variables include Rec, xRec, CurrPage, CurrReport, RequestOptionsPage and CurrFieldNo.
- Access modifiers are internal, local, protected and public, enforced at compile time for tables, fields, codeunits and queries.
- The internalsVisibleTo setting is described alongside internal access.
- XML comments use triple slashes and supported XML tags on codeunits, tables, interfaces and methods.
- XML comments enable IntelliSense and autogenerated help with ALDoc.

## Subtopics

- [Statements](program-building-blocks/statements.md) (2 pages)

## More Learn pages

- [AL operators](https://learn.microsoft.com/dynamics365/business-central/dev-itpro/developer/devenv-al-operators): Describes the operators you can use in AL for Business Central.
- [System-defined variables](https://learn.microsoft.com/dynamics365/business-central/dev-itpro/developer/devenv-system-defined-variables): Describes the system-defined variables that are automatically declared and initialized in AL for Business Central.
- [Using Access Modifiers in AL](https://learn.microsoft.com/dynamics365/business-central/dev-itpro/developer/devenv-using-access-modifiers): Describes how the AL access modifiers can be used in code.
- [XML comments in code](https://learn.microsoft.com/dynamics365/business-central/dev-itpro/developer/devenv-xml-comments): Learn about adding documentation to AL code by including XML elements in a special syntax.

Source: Microsoft Learn (CC BY 4.0). Descriptions are Learn's own.