> For the complete documentation index, see [llms.txt](https://base-tech.gitbook.io/base/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://base-tech.gitbook.io/base/base-bigbang-language/3.-keywords.md).

# 3. Keywords

Keywords are specific terms that have an assigned meaning. Some keywords were introduced in previous chapters, such as true, false, and none. It is important to pay attention to other keywords as well.

### block-height&#x20;

Refers to the current height of the Base blockchain, represented as an unsigned integer. This value can be read at any point in the code, assuming the chain tip is at height 5.

### burn-block-height <a href="#burn-block-height" id="burn-block-height"></a>

This unsigned integer reflects the current block height of the underlying burn blockchain, which in this case is Bitcoin.

### tx-sender <a href="#tx-sender" id="tx-sender"></a>

This field contains the principal that initiated the transaction. It can be utilized to verify the principal calling a public function.

### contract-caller <a href="#contract-caller" id="contract-caller"></a>

The function is called by a principal, which can be either a standard principal or a contract principal. If the contract is directly called through a signed transaction, then the tx-sender and contract-caller will be the same. If the contract calls another contract, then the contract-caller will be the previous contract in the chain.


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter:

```
GET https://base-tech.gitbook.io/base/base-bigbang-language/3.-keywords.md?ask=<question>&goal=<endgoal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal.

The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.