AL extension
An AL extension is an add-on for Business Central developed in the AL language that does not modify the standard code.
AL replaced the earlier C/AL language with the move from Dynamics NAV to Business Central. The decisive difference is in the principle: instead of modifying the standard code, extensions attach to it through defined extension points.
As a result, customisations survive the semi-annual Microsoft updates without having to be merged each time. This is why they are described as upgrade-safe.
In practice this also requires some discipline: not every customisation that was possible in C/AL can be transferred one to one. During an upgrade it is therefore worth checking which customisations the standard now covers by itself.
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