# Error messages > Every diagnostic code the compiler can emit, with its cause, an example and the fix. The Folio compiler never stops at the first problem: it always produces the best presentation it can, plus a list of diagnostics. In the editor, each diagnostic is underlined in the text and listed in the bottom panel, with: | Part | Example | | --- | --- | | Severity | **Error** (something was dropped or does not work) or **warning** (it works, but probably not the way you wanted). | | Code | `F209`. The code is stable and does not change between versions. | | Position | Line and column of the problem. | | Message | unknown attribute: `colr` | | Hint | Did you mean `color`? | Errors inside a component are reported on the line where the component is **used**, with the suffix "(in component `name`)". Errors in a `@style` are reported once, at the definition, not at every use. | Family | Topic | | --- | --- | | [F1xx](#f1xx-structure) | Structure: blocks, tables, code, charts and icons. | | [F2xx](#f2xx-attributes) | Attributes: brace syntax, styles and attribute names. | | [F3xx](#f3xx-values) | Attribute values. | | [F4xx](#f4xx-components) | Components and named slots. | | [F5xx](#f5xx-definitions-and-project-theme) | Preamble definitions and the project theme. | ## F1xx: structure ### F101 · Closing fence with no open block **Error.** Message: `:::` closes a block, but no block is open here. A `:::` alone on a line closes the last open block. Here there is no open block, usually because of an extra `:::`. ```folio # Results We grew 38%. ::: ``` **How to fix:** remove the line or open a block before it, such as `::: columns`. ### F102 · Unclosed block **Error.** Message: block `columns` was opened but never closed. Every block opened with `::: name` needs a `:::` line that closes it. Each slide is read on its own, so the block must be closed before the next `---`. ```folio ::: columns Left Right ``` **How to fix:** add a line containing only `:::` at the end of the block. ### F103 · Definition after the first slide **Error.** Message: `@theme` can only be used at the start of the document, before the first slide. Definitions with `@` (`@title`, `@theme`, `@color`, `@style`, `@component` and the others) only work in the preamble. Once the first slide starts, they are dropped. ```folio # Opening --- @theme ink # Second slide ``` **How to fix:** move the definition to the top of the file, before any content. ### F104 · Block without a name **Error.** Message: missing block name after `:::`. A line that starts with `:::` or `::` and has other content needs the block name right after it. ```folio ::: {.card} Text ::: ``` **How to fix:** write the block name before the attributes, as in `::: box {.card}`. ### F105 · Unclosed code block **Error.** Message: unclosed code block. A code block opened with ` ``` ` needs another ` ``` ` line to end it. Without it, the rest of the slide becomes code. ````folio ```js console.log("hi") ```` **How to fix:** close the block with a line containing ` ``` `. ### F106 · Table without a separator line **Error.** Message: table without a separator line after the header. The second line of a table must be the separator line, which divides the header from the data. ```folio | Product | Price | | Coffee | 12 | ``` **How to fix:** add a line like `| --- | --- |` right below the header. ### F107 · Table row with a different number of columns **Warning.** Message: this row has 3 columns, but the header has 2. A table row has more or fewer cells than the header. ```folio | Product | Price | | --- | --- | | Coffee | 12 | extra | ``` **How to fix:** give every row the same number of cells as the header. To write `|` inside a cell, use `\|`. ### F108 · Unknown block **Error.** Message: unknown block: `colums`. The name after `:::` or `::` is neither a built-in block nor a component defined in the document or the project theme. The hint suggests the closest name. ```folio ::: colums Text ::: ``` **How to fix:** fix the name (here, `columns`) or define the component with `@component`. See the list in [Blocks](/docs/en/reference/blocks/). ### F109 · Single-line block with content **Warning.** Message: `divider` does not accept content; use `:: divider` on a single line. `icon`, `spacer` and `divider` have no content. When opened with `:::`, the content between them and the closing `:::` is ignored. ```folio ::: divider Text ::: ``` **How to fix:** use the single-line form, `:: divider`, and put the text outside the block. ### F110 · Text ignored after the block name **Warning.** Message: the text `3` after `grid` will be ignored. Only `icon` and `spacer` take a value after the name. On the other built-in blocks, loose text is ignored. ```folio ::: grid 3 A B C ::: ``` **How to fix:** use attributes in braces, as in `::: grid {cols=3}`. ### F111 · Chart without a table **Error.** Message: the chart needs a table with the data. The `chart` block draws the data of a Markdown table placed inside it. Without a table, the chart is not drawn. ```folio ::: chart {type=bar} Sales per month ::: ``` **How to fix:** put a table inside the block. The first column holds the labels and the others are the series. See [Charts](/docs/en/guides/charts/). ### F112 · Chart value is not a number **Error.** Message: `twelve` is not a number. Every data cell of a chart, except the first column, must be a number. The invalid cell counts as 0. ```folio ::: chart | Month | Sales | | --- | ---: | | Jan | twelve | ::: ``` **How to fix:** use numbers such as `42`, `3.5` or `3,5`. A trailing `%` is accepted. ### F113 · Chart without series **Error.** Message: the chart table needs at least one column of values. The table only has the label column, so there is nothing to draw. ```folio ::: chart | Month | | --- | | Jan | ::: ``` **How to fix:** add at least one column of values to the table. ### F114 · Icon without a name **Error.** Message: provide the icon name. ```folio :: icon {size=3xl} ``` **How to fix:** write the name after `icon`, as in `:: icon rocket {size=3xl}`. The names are listed in [Icons](/docs/en/reference/icons/). ### F115 · Unknown icon **Error.** Message: unknown icon: `rockets`. The name is not in the list of built-in icons. When there is a similar name, the hint suggests it. ```folio :: icon rockets ``` **How to fix:** use a name from the list in [Icons](/docs/en/reference/icons/), such as `rocket`. ## F2xx: attributes ### F201 · Dot or hash without a name **Error.** Message: `.` must be followed by a name. Inside braces, `.` must be attached to a style name and `#` to an id. ```folio Text {. color=accent} ``` **How to fix:** write the name right after it, as in `{.highlight}` or `{#opening}`, or remove the loose character. ### F202 · Unclosed quotes **Error.** Message: unclosed quotes in attribute value. A value that starts with a quote must end with the same quote. ```folio ![Photo](https://example.com/photo.jpg){fit="cover} ``` **How to fix:** close the value with the quote that opened it: `{fit="cover"}`. At the end of headings, paragraphs and blocks, braces with an open quote are not recognized as attributes and show up as text on the slide. ### F203 · Attribute without a value **Error.** Message: attribute `color` has no value after `=`. There is an `=` with nothing after it. It usually comes with an [F301](#f301--invalid-value), because the empty value is also invalid. ```folio # Heading {color=} ``` **How to fix:** provide the value (`{color=accent}`) or remove the attribute. ### F204 · Invalid text in attributes **Error.** Message: invalid text in attributes: `@highlight`. Inside braces, only `.style`, `#id`, `key=value`, `key="value with spaces"` and `key` are accepted. ```folio Text {@highlight} ``` **How to fix:** use the right form, here `{.highlight}`. Attribute names start with a letter. ### F205 · Id outside the slide separator **Warning.** Message: `#id` only works on the slide separator (--- {#id}). Ids identify slides, for links such as `[back](#opening)`. On other blocks, the id is ignored. ```folio # Opening {#start} ``` **How to fix:** put the id on the slide separator, as in `--- {#start}`. ### F206 · Style that references itself **Error.** Message: style `.loop` references itself. A `@style` includes itself, directly or through other styles. Since the style does not exist yet while its own definition is read, the compiler also shows an [F207](#f207--unknown-style) at the same spot. ```folio @style loop {.loop color=accent} Text {.loop} ``` **How to fix:** remove the circular reference. A style can only include styles defined before it. ### F207 · Unknown style **Error.** Message: unknown style: `.highlite`. The name after the `.` is not a built-in style, a `@style` or a color token. The hint suggests the closest name. ```folio Text {.highlite} ``` **How to fix:** fix the name or declare the style at the start of the document with `@style name {attributes}`. See the [built-in styles](/docs/en/reference/themes/#built-in-styles). ### F208 · Repeated slide id **Warning.** Message: another slide already uses the id `#summary`. Two slides have the same id, so a `#summary` link can only lead to one of them. ```folio --- {#summary} # Summary --- {#summary} # Conclusion ``` **How to fix:** give each slide a different id. ### F209 · Unknown attribute **Error.** Message: unknown attribute: `colr`. The name is neither a style attribute nor an attribute of the block it appears on. The hint suggests the closest name or lists the attributes accepted there. ```folio # Heading {colr=coral} ``` **How to fix:** fix the name. Block attributes, such as `cols` or `fit`, only work on the right blocks. See [Attributes](/docs/en/reference/attributes/). ## F3xx: values ### F301 · Invalid value **Error.** Message: depends on the attribute, for example invalid size: `huge` or unknown color: `corall`. The attribute exists, but the value is not accepted. The attribute is ignored, and the hint says which values are valid. ```folio # Heading {size=huge color=corall} ``` Common cases: | Case | Invalid example | Valid example | | --- | --- | --- | | Unknown color or malformed hex | `color=corall`, `color=#12` | `color=coral`, `color=#123` | | Color opacity outside 0 to 100 | `color=accent/150` | `color=accent/40` | | Name outside the scale or number out of range | `size=huge`, `pad=900` | `size=5xl`, `pad=xl` | | Font not declared | `font=title` | `font=display` or `@font title …` | | Invalid weight | `weight=450` | `weight=500` | | Invalid boolean | `italic=maybe` | `italic` or `italic=false` | | Invalid alignment | `align=middle` | `align=center` | | Invalid shadow | `shadow=xl` | `shadow=lg` | | Border wider than 40 | `border="80 coral"` | `border="4 coral"` | | Invalid length | `w=200%`, `w=half` | `w=50%`, `w=480` | | Attribute that needs a value, used alone | `{size}` | `{size=xl}` | | Address not allowed in a link or image | `[x](javascript:…)`, `![x](file.png)` | `https://…`, `asset:` | | Invalid image fit | `fit=stretch` | `fit=cover` | | Grid columns outside 1 to 12 | `cols=20` | `cols=4` | | Invalid column proportions | `widths="a b"` | `widths="2 1"` | | Invalid chart type | `type=radar` | `type=line` | | Invalid `spacer` size | `:: spacer huge` | `:: spacer 3xl` | | Step outside 1 to 99 | `step=0` | `step=1` | **How to fix:** use one of the values given in the hint. The full scales and ranges are in [Attributes](/docs/en/reference/attributes/). ### F302 · `widths` does not match the columns **Warning.** Message: `widths` has 3 values, but there are 1 columns. The number of proportions in `widths` differs from the number of children of the `columns` block. ```folio ::: columns {widths="2 1 1"} Left ::: ``` **How to fix:** give one proportion per column, or adjust the columns. Remember that each direct child is a column; group several elements with `::: stack`. ## F4xx: components ### F401 · `$content` outside a component **Error.** Message: `$content` can only be used inside a @component. `$content` marks where the content passed to a component goes, so it only makes sense in the body of a `@component`. ```folio # Heading $content ``` **How to fix:** remove the line or move it into a component body. To write the literal text, use `\$content`. ### F404 · Component that uses itself **Error.** Message: component `echo` uses itself. A component uses itself, directly or through other components. Components have no recursion, so the use is dropped. ```folio @component echo :: echo @end :: echo ``` **How to fix:** remove the circular use from the component body. ### F405 · Components nested too deeply **Error.** Message: components nested too deeply (limit: 16 levels). A component uses another, which uses another, and so on, for more than 16 levels. The example below is abbreviated: with all 17 definitions written out, the error shows up on the use of `n1`. ```folio @component n1 :: n2 @end @component n2 :: n3 @end // n3 to n16 follow the same pattern, each one using the next @component n17 End @end :: n1 ``` **How to fix:** simplify the chain of components by merging intermediate levels. ### F406 · Style or id on a component use **Error.** Message: components only accept parameters, not .styles or #id. When using a component, the braces only accept named parameters. ```folio @component badge {text} ::: box {.card} $text ::: @end :: badge {.dark text=New} ``` **How to fix:** wrap the component in a block with the style (`::: box {.dark}` … `:: badge {text=New}` … `:::`) or add a parameter for it. ### F407 · Unknown parameter **Error.** Message: component `badge` has no parameter `tone`. The parameter was not declared in the component definition. The hint lists the existing parameters. ```folio @component badge {text} ::: box {.card} $text ::: @end :: badge {text=New tone=accent} ``` **How to fix:** fix the name or declare the parameter, as in `@component badge {text tone=accent}`. ### F408 · Loose text after the component name **Error.** Message: components take named parameters in braces. Components do not take positional values: every parameter needs a name. ```folio @component badge {text=New} ::: box {.card} $text ::: @end :: badge Sale ``` **How to fix:** pass the value as a named parameter: `:: badge {text=Sale}`. ### F409 · Missing required parameter **Error.** Message: missing required parameter `text` of component `badge`. Parameters declared without a default value are required. ```folio @component badge {text} ::: box {.card} $text ::: @end :: badge ``` **How to fix:** provide the parameter (`:: badge {text=New}`) or give it a default value in the definition (`@component badge {text=New}`). ### F410 · Undeclared `$` placeholder **Error.** Message: component `badge` uses `$title`, which is not a declared parameter. The component body uses `$title` inside text or an attribute, but `title` is not in the parameter list. ```folio @component badge {text} ::: box {.card} ## $title $text ::: @end :: badge {text=New} ``` **How to fix:** declare the parameter (`@component badge {text title}`) or fix the name. Alone on a line, `$name` is a named slot and does not cause this error. ### F411 · Content ignored by the component **Warning.** Message: component `badge` does not use `$content`; the content will be ignored. The component was used with `:::` and received content, but its body has no `$content`. ```folio @component badge {text} ::: box {.card} $text ::: @end ::: badge {text=New} This paragraph is ignored. ::: ``` **How to fix:** add `$content` to the component body or use the single-line form (`:: badge {text=New}`). ### F412 · Built-in block name **Error.** Message: `box` is already a language block and cannot be redefined. The names `stack`, `row`, `columns`, `grid`, `box`, `steps`, `notes`, `chart`, `icon`, `spacer`, `divider` and `slot` are reserved. ```folio @component box Text @end ``` **How to fix:** pick another name, such as `panel` or `card-box`. ### F413 · Component defined twice **Error.** Message: component `badge` was defined more than once. The same document defines two components with the same name. The second definition is dropped. ```folio @component badge New @end @component badge Sale @end ``` **How to fix:** remove or rename one of the definitions. Redefining a project theme component in a presentation is allowed and does not cause this error. ### F414 · Unknown named slot **Error.** Message: component `pair` has no slot `side-c`. `::: slot` fills a slot that the component does not declare. The hint suggests the closest name. ```folio @component pair {title} ## $title $content $side-b @end ::: pair {title=Comparison} Before ::: slot side-c After ::: ::: ``` **How to fix:** use the name of an existing slot (here, `side-b`) or declare the slot in the component with `$side-c` alone on a line. ### F415 · `::: slot` without a name **Error.** Message: provide the slot name. ```folio @component pair {title} ## $title $content $side-b @end ::: pair {title=Comparison} Before ::: slot After ::: ::: ``` **How to fix:** write the slot name after `slot`, as in `::: slot side-b`. ### F416 · `::: slot` outside a component **Error.** Message: `::: slot` can only be used inside a component. `::: slot` only works as a direct child of a container component use. Outside one, the compiler also warns that the name is ignored ([F110](#f110--text-ignored-after-the-block-name)). ```folio ::: slot side-b After ::: ``` **How to fix:** put the `::: slot` inside `::: component` … `:::`, or remove the block. ### F417 · Slot filled twice **Error.** Message: slot `side-b` was filled more than once. ```folio @component pair {title} ## $title $content $side-b @end ::: pair {title=Comparison} ::: slot side-b After ::: ::: slot side-b Again ::: ::: ``` **How to fix:** merge the content into a single `::: slot side-b`. ## F5xx: definitions and project theme ### F501 · Definition without a value **Error.** Message: `@title` needs a value. `@title`, `@author`, `@theme`, `@version` and `@aspect` need a value on the same line. ```folio @title # Opening ``` **How to fix:** provide the value, as in `@title Annual report`, or remove the line. ### F502 · Incomplete `@color` **Error.** Message: `@color` expects a name and a value. ```folio @color # Opening ``` **How to fix:** provide the token name and the color, as in `@color brand #ff6b4a`. ### F503 · Incomplete `@style` **Error.** Message: `@style` expects a name and attributes. ```folio @style highlight # Opening ``` **How to fix:** provide the name and the attributes in braces, as in `@style highlight {color=coral weight=bold}`. ### F504 · Block without `@end` **Error.** Message: `@component` without `@end` (or `@header`, `@footer`). Without `@end`, the rest of the document is read as the block body, and the presentation ends up with no slides. ```folio @component badge {text} ::: box {.card} $text ::: # Opening ``` **How to fix:** end the `@component`, `@header` or `@footer` with an `@end` line. ### F505 · `@end` without an open block **Error.** Message: `@end` without an open block. An `@end` line appears with no open `@component`, `@header` or `@footer` before it. ```folio @end # Opening ``` **How to fix:** remove the `@end` or add, before it, the `@component`, `@header` or `@footer` it should close. ### F506 · Unknown definition **Error.** Message: unknown definition: `@theem`. The name after `@` is not a language definition. The hint suggests the closest one. ```folio @theem ink # Opening ``` **How to fix:** use one of the definitions: `@title`, `@author`, `@theme`, `@version`, `@aspect`, `@color`, `@font`, `@style`, `@component`, `@header`, `@footer` or `@end`. ### F507 · Font name without closing quotes **Error.** Message: font name without closing quotes. ```folio @font title "Bebas Neue 400 # Opening ``` **How to fix:** close the quotes after the family name: `@font title "Bebas Neue" 400`. ### F508 · Invalid font family **Error.** Message: invalid font name: `Open-Sans`. The family name can only contain letters, numbers and spaces, and cannot be empty. ```folio @font title "Open-Sans" # Opening ``` **How to fix:** use the family name as it appears on Google Fonts, in quotes: `@font title "Open Sans"`. ### F509 · Invalid font weight **Error.** Message: invalid font weight: `450`. ```folio @font title "Inter" 450 # Opening ``` **How to fix:** use weights from 100 to 900, in steps of 100, such as `400` or `500`. ### F510 · Component without a name **Error.** Message: `@component` needs a name. ```folio @component {text} $text @end ``` **How to fix:** write the name right after `@component`: `@component badge {text}`. ### F511 · Invalid component name **Error.** Message: invalid component name: `Badge`. Component names start with a lowercase letter and use only lowercase letters, numbers and hyphens. ```folio @component Badge {text} $text @end ``` **How to fix:** use a name such as `badge` or `new-badge`. ### F512 · Component parameter with a style or id **Error.** Message: component parameters do not accept .style or #id. The braces after `@component` declare parameters, not styles. ```folio @component badge {.card text} $text @end ``` **How to fix:** remove the `.style` or `#id` from the list and apply the style to a block in the body, such as `::: box {.card}`. ### F513 · Unknown theme **Error.** Message: unknown theme: `dark`. The theme does not exist, and the document falls back to the `paper` theme. ```folio @theme dark # Opening ``` **How to fix:** use `paper`, `ink` or `editorial`. See [Built-in themes](/docs/en/reference/themes/). `@theme` does not create or name a theme: it only picks the base. To have your own theme, keep a base and adjust it with `@color`, `@font` and `@style`. In the Library, the theme's name goes in the **Name** field. See [Themes](/docs/en/guides/themes/). ### F514 · Unsupported language version **Error.** Message: unsupported language version: `2`. ```folio @version 2 # Opening ``` **How to fix:** use `@version 1`, the current version, or remove the line. ### F515 · Unsupported aspect ratio **Error.** Message: unsupported aspect ratio: `21:9`. ```folio @aspect 21:9 # Opening ``` **How to fix:** use `16:9` (the default) or `4:3`. ### F516 · Invalid color name **Error.** Message: invalid color name: `Brand`. Color tokens start with a lowercase letter and use only lowercase letters, numbers and hyphens. ```folio @color Brand #ff6b4a # Opening ``` **How to fix:** use a name such as `brand` or `brand-dark`. ### F517 · Invalid font token name **Error.** Message: invalid font name: `Title`. The token name (the first word after `@font`) follows the same rule as color tokens. ```folio @font Title "Bebas Neue" 400 # Opening ``` **How to fix:** use a name such as `title`, and apply it with `{font=title}`. ### F518 · Invalid style name **Error.** Message: invalid style name: `Highlight`. ```folio @style Highlight {color=accent weight=bold} # Opening ``` **How to fix:** use lowercase letters, numbers and hyphens, such as `highlight`. ### F519 · Slides in the project theme **Error.** Message: the project theme can only contain definitions, not slides. It only appears in the [project theme](/docs/en/guides/themes/) editor, never in presentations. The example below is the text of the project theme. ```folio @theme ink @color brand #12a37f # Opening ``` **How to fix:** keep only lines that start with `@` (`@theme`, `@color`, `@font`, `@style` and `@component`) in the theme, plus blank lines and comments. Slide content goes in each presentation. ### F520 · `@title` or `@author` in the project theme **Warning.** Message: `@title` in the project theme is ignored; set it in each presentation. It only appears in the project theme editor. Title and author belong to each presentation, so they are ignored in the theme. ```folio @title Annual report @theme ink ``` **How to fix:** remove the line from the theme and write `@title` or `@author` at the start of each presentation. ### F521 · Repeated `@header` or `@footer` **Error.** Message: `@footer` was defined more than once. Each presentation has one header and one footer. The second block is ignored. ```folio @footer Confidential @end @footer $page / $pages @end # Opening ``` **How to fix:** put all the content in a single block, for example with `::: columns`. See [Header and footer](/docs/en/guides/header-footer/). ### F522 · Unknown field in the header or footer **Error.** Message: `@footer` uses `$pagina`, which is not an available field. Inside `@header` and `@footer`, `$` followed by a name is an automatic field. The hint suggests the closest field. ```folio @footer Page $pagina @end # Opening --- # Agenda ``` **How to fix:** use one of the fields: `$page`, `$pages`, `$title`, `$author` or `$date`. ### F523 · Step-by-step reveal in the header or footer **Warning.** Message: `@footer` is always shown in full; `step` and `::: steps` are ignored in it. ```folio @footer ::: steps - First - Second ::: @end # Opening --- # Agenda ``` **How to fix:** remove `step` and `::: steps` from the block. To reveal something gradually, do it inside the slide. ### F524 · Notes in the header or footer **Warning.** Message: speaker notes inside `@footer` are ignored. ```folio @footer Confidential ::: notes Remember to mention the contract. ::: @end # Opening --- # Agenda ``` **How to fix:** write `::: notes` inside the slide where the note belongs. ### F525 · Text on the `@header` or `@footer` line **Warning.** Message: the text `Confidential` after `@footer` will be ignored. The `@header` or `@footer` line only accepts attributes in braces. The content goes on the following lines, up to `@end`. ```folio @footer Confidential @end # Opening ``` **How to fix:** move the text to the next line. To turn off the footer that comes from the project theme, use `@footer none`. ### F530 · Definition that does not fit the Library item kind **Error.** Message: `@theme` cannot be used in a palette. Each [Library](/docs/en/guides/library/) item kind accepts only some definitions: palettes take `@color` and `@font`; styles also take `@style`; components also take `@component`; themes accept any theme definition. ```folio @theme paper @color brand #349ef4 ``` **How to fix:** delete the highlighted line or save the item with another kind, for example **Theme** instead of **Palette**. ### F531 · Library item without a main definition **Error.** Message: choose which component is the main one. Library components and styles must say which definition is the main one, the one people call when they use the item. **How to fix:** in the Library editor, pick the **Main definition**. ### F532 · Main definition not found **Error.** Message: component not found: `card`. The chosen main definition does not exist in the item text, or it was renamed. **How to fix:** pick another main definition or fix the name in the text. ### F533 · Unknown item kind **Error.** Message: unknown item kind: `slide`. The item was sent with a kind the Library does not know. Valid kinds are theme, component, style and palette (templates are validated as themes). **How to fix:** save the item again from the app, picking one of the kinds in the list.