https://help.tallysolutions.com/docs/td9rel54/tdl_reference/tdlreference.htm

Tally Definition Language

Tally Definition Language (TDL) is the development language of Tally.ERP 9. TDL is developed to provide the user with the flexibility and power to extend the default capabilities of Tally, and integrate them with the external applications. TDL provides a development platform for the user. The entire user interface of Tally.ERP 9 is built using TDL. TDL as a language, provides capabilities for Rapid Development, Rendering, Data Management, and Integration.

Get started with TDL

Definitions

Data Types

Symbols in TDL

Design using TDL

Objects and Collections

Action and Event framework

Variable Framework

User Defined Fields

Reports, Printing and Validation controls

Functions in TDL

Voucher and Invoice Customisation

To know more about TDL watch Introduction to TallyTechnology and TDL – The Development Language of Tally .