# Syntax Errors

> For the complete documentation index, see [llms.txt](https://plugins.jetbrains.com/docs/intellij/llms.txt).

The IntelliJ Platform provides a mechanism for analyzing the PSI tree and highlighting syntax errors out of the box.

While the PSI tree for the code is being built, a [parser](implementing-parser-and-psi.html) tries to consume tokens according to language grammar. When it encounters a syntax error, like an unexpected token, a [PsiErrorElement](https://github.com/JetBrains/intellij-community/tree/idea/263.7307.200/platform/core-api/src/com/intellij/psi/PsiErrorElement.java) is created and added to the PSI tree with an appropriate error description. In the code analysis daemon, the IDE visits every PSI element in the tree, and when a `PsiErrorElement` is encountered, information about it is collected and used while highlighting the code in the editor.

> **Tip:**
> Additional highlighting can also be added using [Annotators](syntax-highlighting-and-error-highlighting.html#syntax) or Inspections, see [Controlling Highlighting](controlling-highlighting.html) on how to suppress.

## Controlling Syntax Errors Highlighting

In some cases highlighting syntax errors is insufficient or even unnecessary:

* An error can be presented to the user in an easier-to-understand way.

* The actual error cause is in a different location in the code, which is not easily visible when looking at the syntax error.

* An error can be safely ignored in a given context, e.g., incomplete code fragment injected in a Markdown code block.

* A syntax error is not critical and can be considered a warning or even information.

The IntelliJ Platform allows plugins to disable highlighting particular syntax errors. These errors can be optionally handled by additional Annotators or [Inspections](code-inspections.html) if needed.

To control which `PsiErrorElement`s should be reported and which can be ignored, a plugin has to provide an implementation of [HighlightErrorFilter](https://github.com/JetBrains/intellij-community/tree/idea/263.7307.200/platform/analysis-api/src/com/intellij/codeInsight/highlighting/HighlightErrorFilter.java) and register it in the [com.intellij.highlightErrorFilter](https://jb.gg/ipe?extensions=com.intellij.highlightErrorFilter) extension point . It contains a single abstract method `shouldHighlightErrorElement()` which should return `false` if a given `PsiErrorElement` should not be highlighted in the editor.

Examples:

* [HtmlClosingTagErrorFilter](https://github.com/JetBrains/intellij-community/tree/idea/263.7307.200/xml/xml-analysis-impl/src/com/intellij/codeInsight/highlighting/HtmlClosingTagErrorFilter.java) ignoring unmatched closing tag in HTML files

* [MarkdownCodeFenceErrorHighlightingIntention](https://github.com/JetBrains/intellij-community/tree/idea/263.7307.200/plugins/markdown/core/src/org/intellij/plugins/markdown/injection/MarkdownCodeFenceErrorHighlightingIntention.kt) ignoring all syntax errors in a code injected into a Markdown code blocks

See also:

* [Controlling Highlighting](controlling-highlighting.html)