Write one string or choice-token field in cfg by schema key.
Choice tokens (and grid_type/output_format) are lowercased on write,
mirroring read_config_2d's to_lower-on-parse behavior: downstream
dispatch (schemes_2d, boundary_2d/boundary_conditions, resolve_*_scheme)
compares these fields with exact-case ==, so a value set through this
wire-protocol path must land already-normalized.
| Type | Intent | Optional | Attributes | Name | ||
|---|---|---|---|---|---|---|
| type(config_2d_t), | intent(inout), | target | :: | cfg | ||
| character(len=*), | intent(in) | :: | key | |||
| character(len=*), | intent(in) | :: | value | |||
| logical, | intent(out), | optional | :: | is_ok | ||
| character(len=*), | intent(out), | optional | :: | message |