sicher 0.1.1

• Adding the Literal type check
• Adding the extend method to extend a preexisting list schema.
• Adding NonNA() modifier — rejects any value that contains at least one NA.
• Adding Between(min, max) — closed-interval numeric range constraint.
• Adding Matches(pattern) — PCRE regex-constrained string type.
• Adding NonEmpty() modifier — rejects zero-length vectors, lists, and zero-row data frames.

sicher 0.1.0

• Initial CRAN submission.