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syntax_errors.md: minor

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The IntelliJ Platform provides a mechanism for analyzing the PSI tree and highlighting syntax errors out of the box. 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 tries to consume tokens according to language grammar. When it encounters a syntax error, like an unexpected token, a [`PsiErrorElement`](upsource:///platform/core-api/src/com/intellij/psi/PsiErrorElement.java) is created and added to the PSI tree with an appropriate error description. While the PSI tree for the code is being built, a [parser](implementing_parser_and_psi.md) tries to consume tokens according to language grammar.
In the code analysis daemon, the IntelliJ Platform 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. When it encounters a syntax error, like an unexpected token, a [`PsiErrorElement`](upsource:///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.
## Controlling Syntax Errors Highlighting ## Controlling Syntax Errors Highlighting
In some cases highlighting syntax errors is insufficient or even unnecessary: 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. - 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. - 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. - 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 as a warning or even information. - 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.md) if needed. The IntelliJ Platform allows plugins to disable highlighting particular syntax errors.
These errors can be optionally handled by additional Annotators or [Inspections](code_inspections.md) if needed.
To control which `PsiErrorElement`s should be reported and which can be ignored, a plugin has to provide implementation of [`HighlightErrorFilter`](upsource:///platform/analysis-api/src/com/intellij/codeInsight/highlighting/HighlightErrorFilter.java) and register it in the `com.intellij.highlightErrorFilter` extension point. To control which `PsiErrorElement`s should be reported and which can be ignored, a plugin has to provide an implementation of [`HighlightErrorFilter`](upsource:///platform/analysis-api/src/com/intellij/codeInsight/highlighting/HighlightErrorFilter.java) and register it in the `com.intellij.highlightErrorFilter` extension point.
The `HighlightErrorFilter` class contains a single abstract method `shouldHighlightErrorElement()` which should return false if a given `PsiErrorElement` should not be highlighted in the editor. It contains a single abstract method `shouldHighlightErrorElement()` which should return `false` if a given `PsiErrorElement` should not be highlighted in the editor.
**Examples:** **Examples:**
- [`HtmlClosingTagErrorFilter`](upsource:///xml/xml-analysis-impl/src/com/intellij/codeInsight/highlighting/HtmlClosingTagErrorFilter.java) ignoring unmatched closing tag in HTML files - [`HtmlClosingTagErrorFilter`](upsource:///xml/xml-analysis-impl/src/com/intellij/codeInsight/highlighting/HtmlClosingTagErrorFilter.java) ignoring unmatched closing tag in HTML files