Expression concepts
An expression is a user-authored rule that evaluates available data for one security and returns true or false.
The same expression model appears in screeners, Market Automations, and configuration-driven strategies. The surrounding tool decides what a true result means.
Build a comparison
A condition compares a left value with a right value. Inputs can include supported quote fields, financial fields, price bars, standard or custom indicators, and constants. Operators include comparisons such as greater than, less than, equal, and their inclusive variants.
Last Price > 50 is a simple teaching example. It means only that the available last-price value is greater than the constant 50; it is not a trade recommendation.Combine conditions with AND and OR
The visual builder has two nesting levels:
- Conditions inside the same group are alternatives joined by OR.
- Separate groups are requirements joined by AND.
For example, (Price > 50 OR Price < 10) AND Volume > 100000 is true only when the volume requirement and at least one price alternative are true.
Intervals and lookback
Indicators and bars carry their own interval and parameters. A daily moving average and a minute moving average are different inputs even when they use the same period. Values can also require enough historical bars before they become available.
Financial, quote, and bar data update on different schedules. A comparison can therefore mix values with different freshness; review each input rather than assuming they share one timestamp.
The host tool supplies the meaning
| Host | Meaning of true |
|---|---|
| Screener | Include the security in the current result. |
| Market Automation | Create an occurrence only when that security changes from false to true. |
| Trading Strategy | Produce an eligible signal according to its Signal Mode, then apply position and portfolio rules. |
Review and test
Read the generated expression summary, confirm units and intervals, test obvious true and false examples, and inspect real matches. Missing or unavailable data should not be treated as a meaningful false investment signal.
Next: use the Expression Builder.