Write YAML Metadata Block for Quarto Documents

Creates a YAML metadata block that can be dynamically inserted into Quarto documents from R code chunks. This allows setting metadata values based on R computations, which can then be used with Quarto's conditional content features like when-meta and {{< meta >}} shortcodes.

Usage

write_yaml_metadata_block(..., .list = NULL)

Arguments

...: Named arguments to include in the metadata block. Names become the metadata keys and values become the metadata values. These take precedence over any conflicting keys in .list.
.list: Optional list of additional metadata to include. This is useful when you have metadata stored in a list variable. Keys in .list are overridden by any matching keys provided in ....

Value

A character string containing the formatted YAML metadata block, wrapped with knitr::asis_output() so it renders as raw markdown. Returns NULL invisibly if no metadata is provided.

Details

The function converts R values to YAML format and wraps them in YAML delimiters (---). Logical values are converted to lowercase strings ("true"/"false") to ensure compatibility with Quarto's metadata system.

When both ... and .list contain the same key, the value from ... takes precedence and will override the value from .list.

If no metadata is provided (empty ... and NULL or empty .list), the function returns NULL without generating any output.

This addresses the limitation where Quarto metadata must be static and cannot be set dynamically from R code during document rendering.

YAML 1.2 Compatibility:

To ensure compatibility with Quarto's YAML 1.2 parser (js-yaml), the function automatically handles two key differences between R's yaml package (YAML 1.1) and YAML 1.2:

Boolean values:

R logical values (TRUE/FALSE) are converted to lowercase YAML 1.2 format (true/false) using [yaml::verbatim_logical()]. This prevents YAML 1.1 boolean representations like yes/no from being used.

String quoting:

Strings with leading zeros that contain digits 8 or 9 (like "029", "089") are automatically quoted to prevent them from being parsed as octal numbers, which would result in data corruption (e.g., "029" becoming 29). Valid octal numbers containing only digits 0-7 (like "0123") are handled by the underlying yaml package.

For manual control over string quoting behavior, use [yaml_quote_string()].

Quarto Usage:

To use this function in a Quarto document, create an R code chunk with the output: asis option:

```{r}
#| output: asis
write_yaml_metadata_block(admin = TRUE, version = "1.0")


Without the `output: asis` option, the YAML metadata block will be
displayed as text rather than processed as metadata by Quarto.


[yaml::verbatim_logical()]: R:yaml::verbatim_logical()
[yaml_quote_string()]: R:yaml_quote_string()

Examples

if (FALSE) { # \dontrun{
# In a Quarto document R chunk with `#| output: asis`:
admin <- TRUE
user_level <- "advanced"

# Set metadata dynamically
write_yaml_metadata_block(
  admin = admin,
  level = user_level,
  timestamp = Sys.Date()
)

# Strings with leading zeros are automatically quoted for YAML 1.2 compatibility
write_yaml_metadata_block(
  zip_code = "029",    # Automatically quoted as "029"
  build_id = "0123"    # Quoted by yaml package (valid octal)
)

# Use with .list parameter
metadata_list <- list(version = "1.0", debug = FALSE)
write_yaml_metadata_block(.list = metadata_list)

# Direct arguments override .list values
base_config <- list(theme = "dark", debug = TRUE)
write_yaml_metadata_block(
  debug = FALSE,  # This overrides debug = TRUE from base_config
  author = "John",
  .list = base_config
)

# Then use in Quarto with conditional content:
# ::: {.content-visible when-meta="admin"}
# Admin-only content here
# :::
} # }