> For the complete documentation index, see [llms.txt](https://help.openloyalty.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://help.openloyalty.io/implementation-guide/integrations-and-data-exchange/expressions.md).
# Expressions
In this section, you will learn about Open Loyalty language and more complex campaign conditions.
### **Introduction to Open Loyalty Language**
\
When setting up conditions and effects for rules in [Campaigns](https://help.openloyalty.io/campaigns), you may find that some situations are not covered by premade values. However, you are not limited to using these values - you can use an Open Loyalty language to create very specific conditions and values. \
\
In conditions, you can find a condition called **Expressions**.
You can set the value of such an expression. It can be set as a combination of attributes and operators using the meta language created by Open Loyalty. It allows you to create a fully customizable condition that meets the rules of your planned loyalty program.
For example, you can create a campaign that is triggered when a customer buys a product from a certain category. You can do it in two ways:
Set a premade condition:
Or use an expression:
In the same way, you can create custom campaign effects - you can use premade values, or enter them yourself:
In this section, you will find a description of the meta-language together with all the supported syntaxes, which is based on the expression syntax of Symfony Expression.
***
#### **The component supports**
* strings - single and double quotes (e.g. 'hello')
* numbers - integers (e.g. 103), decimals (e.g. 9.95), decimals without leading zeros (e.g. .99, equivalent to 0.99); all numbers support optional underscores as separators to improve readability (e.g. 1\_000\_000, 3.14159\_26535)
* arrays - using JSON-like notation (e.g. \[1, 2])
* hashes - using JSON-like notation (e.g. { foo: 'bar' })
* booleans - true and false
* null - null
* exponential - also known as scientific (e.g. 1.99E+3 or 1e-2)
---
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