What is an XLA file?
A file with .xla extension is a Microsoft Excel Add-Ins file format that adds modules, extra functions, and other tools to Microsoft Excel. The Ad-Ins provide additional functionality to Excel spreadsheets and are supported in version 2007 or later. XLA files have mime media type application/vnd.ms-excel. These can be opened using Microsoft Excel that is available for Windows as well as MacOS.
XLA File Format
XLA files are based on binary data format. However, further information about its file format specifications are not available. General assumption is that XLA follow the [MS-XLS] - Excel Binary File Format Structure.